# Building a hybrid Unified CM and Webex Calling environment for a phased migration

Systems: Cisco Unified CM to Webex Calling

For Voice engineers and administrators configuring hybrid call routing and migrating users from Cisco Unified CM to Webex Calling.

Canonical: https://warmtransfer.net/guides/cucm-webex-calling-hybrid-build

Last verified: 2026-09-24

During a migration between Cisco Unified CM and Webex Calling, dual call control allows both environments to coexist while endpoints move site by site[^70][^71]. Interconnecting the two environments through a Local Gateway maintains internal dialing and PSTN reachability across the deployment[^23][^72].

## Before you start

- Ensure you have administrator access to Cisco Unified CM Administration and Control Hub[^56].
- Verify that IP phones intended for migration run firmware 14.1 or later[^41].
- Note that 8821 and 8831 models cannot be migrated[^1].
- Ensure 8800-series hardware version V15 or later devices run at least MPP firmware 11.3.3[^1].
- Confirm one-way network latency between the Local Gateway and the Webex Calling access SBC does not exceed 100 ms[^73].
- Verify temporary coexistence licensing, such as PID A-FLEX-P-CALL providing up to 18 months of coverage[^74].

## What changes by situation

- Where does the Local Gateway function run? Shared on the existing PSTN CUBE; Dedicated separate CUBE for Local Gateway.
- What kind of Local Gateway trunk will you use? Registration-based trunk; Certificate-based trunk.
- How will telephone numbers move to Webex Calling? Site-by-site transition using premises-based PSTN; All at once via Cloud Connected PSTN and route lists.
- Where are the migrating sites located? United States, US territories, or Canada; Other regions.

## Step 1: Assess the estate and plan migration batches

### Do
Analyze your existing Unified CM environment using the Control Hub Migration Insights tool by uploading Unified CM TAR export files and CDR data[^29]. Group users and endpoints into migration batches by physical site or department[^28]. Keep dependent users together in the same batch, including users sharing line appearances, call pickup groups, hunt groups, BLF monitoring, call park numbers, intercom, or executive-assistant relationships[^33][^75]. Size the interconnect between Unified CM and Webex Calling to support expected concurrent calls and required redundancy[^25][^76].

### Verify
Review the Migration Insights output to verify device eligibility, feature usage, shared lines, and hunt groups[^29]. Confirm all members of identified feature dependency groups reside within the same scheduled batch[^33].

## Step 2: Provision users and create Webex Calling locations

**Site-by-site transition using premises-based PSTN**

### Do
Provision all enterprise users in Webex at or before the project start, including those not yet moving calling control[^65]. Configure each target location in Control Hub with premises-based PSTN routed through the Local Gateway, adhering to the rule that each location supports only one PSTN type[^38][^77]. Assign at least two DIDs per location: a main number and a voice portal pilot number[^60][^66]. Ensure the location has a main number assigned whenever trunks or extension-only entities are configured[^27].

### Verify
Verify that each configured location displays premises-based PSTN in Control Hub and has an active main telephone number[^27][^38]. Confirm directory search is functional across provisioned users[^65][^78].

### Rollback
Suggested rollback: delete unassigned numbers from the location and remove the location profile in Control Hub.

**All at once via Cloud Connected PSTN and route lists**

### Do
Provision all enterprise users in Webex at or before the project start[^65]. Procure and order numbers from the Cloud Connected PSTN provider before entering them into Control Hub[^39]. Create locations configured for Cloud Connected PSTN[^38]. Assign a main number and voice portal number per location[^60][^27]. Procure the Route List Calls add-on license to cover off-premises call volumes generated by on-premises Unified CM users[^51].

### Verify
Verify that the location indicates Cloud Connected PSTN in Control Hub[^38]. Verify that the licensed Route List Calls capacity accommodates peak off-net call volume within the allowed 20% burst headroom[^51].

### Rollback
Suggested rollback: remove configured numbers from Control Hub once they are unassigned.

## Step 3: Build the Local Gateway trunk in Control Hub and on the CUBE

**Registration-based trunk**

### Do
Establish Local Gateway trunks before building dial plans[^59]. Ensure the CUBE platform runs Cisco IOS XE 17.6.1a or later, with 17.12.2 or later recommended[^45][^22]. In Control Hub, create a registration-based trunk supporting up to 250 concurrent calls, noting the assigned digest authentication credentials[^45]. Configure the CUBE with SIP over TLS signaling, SRTP media encryption, and digest credentials matching Control Hub[^26][^45]. Enable dual-identity and P-Charge-Info support on the trunk[^13]. Create a route group holding 1 to 10 trunks, and designate the route group as the routing destination[^46][^47].

### Verify
Navigate to Calling > Call Routing > Trunk in Control Hub to verify that the trunk displays an online status, which refreshes every 3 minutes[^58].

### Rollback
Delete the registration trunk in Control Hub after removing it from associated route groups, as trunks can only be deleted when not in use[^57].

**Certificate-based trunk**

### Do
Establish Local Gateway trunks before building dial plans[^59]. Ensure the CUBE runs Cisco IOS XE 17.9.1a or later, with 17.12.2 or later recommended, or use an approved third-party SBC[^7][^22]. Claim the domain in Control Hub, and publish a public DNS A or SRV record resolving the gateway FQDN[^7]. Add a certificate-based trunk configured with the FQDN[^7]. On the SBC, configure SIP over TLS and SRTP[^26]. Enable dual-identity and P-Charge-Info on the trunk[^13]. Assign the trunk to a route group containing up to 10 trunks[^46][^47].

### Verify
Check Calling > Call Routing > Trunk in Control Hub to confirm the trunk reports an online status[^58].

### Rollback
Remove the trunk from all route groups and delete the trunk configuration in Control Hub[^57].

## Step 4: Connect Unified CM to the Local Gateway

**Shared on the existing PSTN CUBE**

### Do
Verify that the gateway does not run Cisco Unified CME, as CME and Local Gateway cannot co-locate on the same vCUBE instance[^34]. Maintain existing PSTN routing without disruption[^24]. In Unified CM, configure two separate SIP trunks directed to the gateway using different SIP listening ports: port 5060 for PSTN traffic and port 5065 for Webex Calling traffic[^8][^43]. On the CUBE, configure dial-peers to route calls from Unified CM on port 5065 to Webex Calling and calls on port 5060 to the PSTN[^43]. Assign inbound calls from Webex a calling search space accessing partitions for DN (+E.164 directory numbers), ESN (abbreviated inter-site dialing), PSTN access (PSTNInternational), and onNetRemote[^9][^79]. Ensure this inbound calling search space does not have access to the Webex Calling partition to prevent call loops[^80].

### Verify
Verify that existing inbound and outbound PSTN calls on port 5060 continue to complete normally[^43]. Place a test call across the port 5065 trunk from Unified CM and confirm it routes to the Local Gateway dial-peer for Webex Calling[^43].

### Rollback
Suggested rollback: delete the dial-peers on the gateway and remove the SIP trunk from the call control platform.

**Dedicated separate CUBE for Local Gateway**

### Do
Configure the dedicated Local Gateway platform solely for Webex Calling interconnect with no pre-existing voice routing[^24]. On Unified CM, configure a SIP trunk pointing to the dedicated Local Gateway platform using port 5065[^43]. Place the trunk in a dedicated route group and route list[^63]. Assign inbound calls from Webex a calling search space containing partitions for DN, ESN, PSTNInternational, and onNetRemote[^9][^79]. Ensure the incoming CSS lacks access to the Webex Calling partition to avoid routing loops[^80].

### Verify
Suggested check: verify trunk signaling status shows in service on Unified CM and place a test call over the dedicated route list[^63].

### Rollback
Suggested rollback: remove the route list, route group, and SIP trunk associated with the dedicated Local Gateway in Unified CM[^63].

## Step 5: Extend the Unified CM dial plan to reach Webex Calling

### Do
Create a dedicated partition on Unified CM for Webex Calling destinations[^68][^81]. Within this partition, configure full +E.164 route patterns covering the Webex Calling DID ranges, pointing to the route list for the Local Gateway trunk[^63]. Configure dial plan patterns for +E.164, intra-site extension dialing, inter-site extension dialing when extension ranges are unique, abbreviated inter-site dialing, and forced on-net dialing to Webex Calling[^62][^82]. Configure abbreviated inter-site dialing normalization to translate enterprise numbers to +E.164 before matching the Webex partition[^83]. Add the Webex Calling partition to all calling search spaces requiring access to Webex users, including the inbound PSTN trunk CSS[^69].

### Verify
From a Unified CM phone, place test calls to a provisioned Webex destination using +E.164, internal extension, and site code plus extension formats[^62]. Place an inbound test call from the PSTN to a Webex Calling DID traversing Unified CM[^69]. Confirm that Unified CM best-match routing leaves calls to active on-premises DNs on the local system[^84].

### Rollback
Remove the Webex partition from all calling search spaces and delete the Webex route patterns[^69].

## Step 6: Build the Webex Calling dial plan toward Unified CM

### Do
Configure an organization-wide internal extension length between 2 and 10 digits to match Unified CM extensions[^19][^85]. Set a location routing prefix with uniform site code lengths across locations[^53][^86]. Ensure no internal extension ranges begin with designated inter-site or PSTN steering digits[^87]. Enable the setting to allow extension dialing between locations only if all extensions across the enterprise are unique[^18][^88]. For overlapping extension ranges, prefix extensions with an access code and site code[^89]. In the US, add a padding digit if 7-digit internal numbering overlaps with local 7-digit PSTN dialing[^54]. Create enterprise dial plans containing only on-premises destination patterns, using the exclamation mark or X wildcard (not combined in a single pattern), pointing to the Local Gateway route group[^12][^11][^90]. Enable Calls to On-Premises Extensions per location using Standard Behavior, and configure the Maximum Unknown Extension Length[^64][^91].

### Verify
From a Webex Calling test endpoint, place test calls to Unified CM users by dialing +E.164, site code plus extension, and standalone extension formats[^64][^92]. Verify that call-back operations from the missed calls directory on Unified CM reach Webex endpoints[^93].

### Rollback
Suggested rollback: disable Calls to On-Premises Extensions and delete the enterprise dial plans from Control Hub[^64].

## Step 7: Stage the numbers

**Site-by-site transition using premises-based PSTN**

### Do
Add the phone numbers for the next batch to the location in Control Hub with the Activate Numbers Later option selected, keeping them inactive in call routing[^20][^3]. Assign these staged inactive numbers to users or features ahead of migration[^21]. Coordinate port orders closely to account for carrier processing lead times and concurrent request limitations[^40][^94].

### Verify
Confirm that staged numbers appear in Control Hub with an inactive status and remain inactive after being assigned to users[^21].

### Rollback
Unassign the staged numbers and delete them from the location inventory in Control Hub[^10].

**All at once via Cloud Connected PSTN and route lists**

### Do
For users remaining on Unified CM, configure their numbers in a Webex Calling route list assigned to a route group pointing to the enterprise Local Gateway[^50][^52]. Configure Unified CM to send an outbound calling party number that matches an E.164 number configured in the route list[^48]. Ensure off-net calling routes through the location's PSTN connection[^50][^95].

### Verify
Place an inbound call to a number assigned to the route list and verify that Webex Calling delivers the call to Unified CM[^50]. Place an outbound PSTN call from a Unified CM user whose calling party number matches the route list entry[^50][^48].

### Rollback
Suggested rollback: remove the numbers from the Webex Calling route list in Control Hub[^50].

## Step 8: Configure emergency calling for the site

**United States, US territories, or Canada**

### Do
Ensure that every location maintains at least basic emergency calling with at least one customer-owned +E.164 number assigned[^5]. Configure an emergency callback number (ECBN) for each user using their assigned number, the location default ECBN, or another assigned location number[^16]. Set and validate the physical location address in Control Hub to populate PIDF-LO metadata on emergency calls[^4]. Enable enhanced emergency calling (RedSky), routing emergency traffic to the E911 provider rather than the Local Gateway[^15][^14]. If route lists are deployed, enable RedSky on the route list location[^49]. Ensure that a user can dial 911 directly from any station without any additional digit, code, prefix or post-fix[^30]. Configure internal emergency notifications and dispatchable location handling[^32][^31].

### Verify
Suggested check: place test calls to emergency services from both a migrated endpoint and an on-premises endpoint. Verify that internal notifications trigger upon dialing 911 and dispatchable address information is correctly delivered[^32][^31].

### Rollback
Suggested rollback: do not remove emergency calling configurations; modify policies forward only after confirming alternate routing paths.

**Other regions**

### Do
Ensure at least basic emergency calling is configured with a customer-owned +E.164 number assigned to the location[^5]. Route emergency calls across the location's PSTN connection[^15]. Configure each user's ECBN using their direct number, the location default ECBN, or an assigned location number so that public safety systems receive caller-ID-derived site location[^6][^16].

### Verify
Place an emergency test call from a migrated endpoint and verify that the asserted caller ID reflects the user's assigned site callback number[^6].

### Rollback
Suggested rollback: preserve emergency routing settings and adjust destination parameters forward only.

## Step 9: Prepare Webex Calling voicemail for the site

### Do
Configure the voicemail pilot (voice portal) number for the location in Control Hub[^66]. Plan for separate voicemail infrastructure, as Webex Calling native voicemail cannot integrate with Cisco Unity Connection[^36][^96]. Notify migrating users that existing Unity Connection voicemail messages and personal greetings cannot be transferred natively and must be re-recorded[^37][^97].

### Verify
Verify that voicemail boxes are properly assigned and can be accessed both internally and externally via the voice portal number[^67].

### Rollback
Suggested rollback: retain the mailbox configuration on the on-premises system until migration testing succeeds.

## Step 10: Move the batch's users and phones

### Do
Confirm phones are running firmware 14.1 or later prior to migration[^41][^98]. Execute the migration in Control Hub using the Unified CM migration tool, adhering to limits of up to 1000 users and 1000 devices per migration task[^56][^99]. Migrate user feature configurations including line layouts, shared lines, call queues, hunt groups, and virtual lines[^100]. Complete phone conversion either automatically by pointing phones to a TFTP server or manually by uploading generated BAT files into Unified CM Bulk Administration[^42]. Exclude the 8821 and 8831 from the task[^1].

### Verify
Suggested check: In Control Hub, confirm the migrated phones and user configurations appear as expected.

### Rollback
Suggested rollback: phones cannot be downgraded below minimum supported versions once converted, requiring manual reconfiguration to restore on-premises phone loads.

## Step 11: Cut the site over and run acceptance tests

**Site-by-site transition using premises-based PSTN**

### Do
Activate the staged numbers in Control Hub, either individually or in batches of up to 500 numbers[^21]. Execute acceptance testing across a representative subset of migrated users[^2].

### Verify
Confirm that inbound and outbound PSTN calls route successfully to users, hunt groups, call queues, and auto attendants[^2]. Test internal extension calls between migrated Webex users and remaining Unified CM users across the Local Gateway[^23]. Confirm voicemail access and deposit operate as expected[^67].

### Rollback
Suggested rollback: reactivate call routing on directory numbers if cutover validation fails.

**All at once via Cloud Connected PSTN and route lists**

### Do
Execute acceptance testing on a representative subset of cutover users[^2].

### Verify
Verify that inbound and outbound PSTN calls route properly through Cloud Connected PSTN to users, auto attendants, hunt groups, and call queues[^2]. Verify inter-system calls between Webex Calling and Unified CM complete across the Local Gateway[^23]. Verify voicemail retrieval and deposit[^67].

### Rollback
Suggested rollback: preserve on-premises directory numbers until validation testing passes.

## Step 12: Clean up Unified CM and decommission

### Do
Following successful cutover of the batch, disable or delete directory numbers, line appearances, and calling features on Unified CM for migrated users and devices[^61][^101]. Ensure all video endpoints and remaining phones are migrated to Webex before decommissioning Unified CM server nodes[^17]. When all sites have migrated and dual call control is concluded, delete unneeded Local Gateway trunks and unassigned numbers in Control Hub[^57][^10].

### Verify
Verify that deleted directory numbers are no longer present in Unified CM routing tables[^61]. Verify that unused trunks are successfully removed from Control Hub after their route groups are dismantled[^57].

### Rollback
Suggested rollback: disable directory numbers temporarily before permanent deletion to simplify recovery during cleanup[^61].

## Applicability

Applies to: Cisco IP Phone 8800, Cisco Webex Calling, Cisco Webex Calling Local Gateway, Cisco Unified CM, Cisco CUBE Local Gateway, Cisco Webex Control Hub, Multi-line telephone systems, Cisco IP Phone 7800, Cisco Webex, Cisco Webex Calling Customer Assist, Cisco Webex App, Cisco Collaboration Flex Plan, Cisco Local Gateway, and Cisco Webex Calling migration tool. Deployments: on-premises and multi-tenant. Sources checked 2026-09-25. Cisco Unified CM version support covers clusters on release 14 or 15 with SUs or later when deploying Webex Calling Customer Assist[^102]. Local Gateway requirements specify Cisco IOS XE 17.6.1a or later for registration-based trunks, 17.9.1a or later for certificate-based trunks, and recommend 17.12.2 or later across both types[^45][^7][^22]. Enhanced emergency calling using RedSky is limited to the United States, its territories, and Canada[^15].

## What remains uncertain

The exact procedure to transition an active telephone number out of a Webex Calling route list directly to an individual Webex user is not covered by the sources below. The specific Control Hub mechanism to return an activated number back to an inactive state following a failed cutover is not covered by the sources below.

## Sources

[^1]: 8800-series phones of hardware version V15 or later need at least MPP firmware 11.3.3 and cannot downgrade to earlier MPP firmware; the 8821 and 8831 cannot be migrated. Source: [Migrate your phone to Webex Calling](https://help.webex.com/en-us/article/n19c71/Migrate-your-phone-to-Webex-Calling), Supported phone models. Checked 2026-09-24.
[^2]: After migrating a group of users Cisco says to test a subset of them, including end-to-end inbound and outbound PSTN calls delivered to users, call queues, hunt groups and auto attendants. Source: [Implement the migration from Unified CM to Webex Calling](https://help.webex.com/en-us/article/q0pgpb/Implement-the-migration-from-Unified-CM-to-Webex-Calling), Acceptance testing. Checked 2026-09-24.
[^3]: When adding numbers in Control Hub, turning on Activate Numbers Later makes them available for configuration immediately while leaving activation for later, which Cisco says to use when porting numbers later. Source: [Manage phone numbers in Control Hub](https://help.webex.com/en-us/article/wkj3f0/Manage-phone-numbers-in-Control-Hub), Add phone numbers. Checked 2026-09-24.
[^4]: In the US and Canada the Webex Calling location address is validated and used to send PIDF-LO location information with emergency calls. Source: [Implement the migration from Unified CM to Webex Calling](https://help.webex.com/en-us/article/q0pgpb/Implement-the-migration-from-Unified-CM-to-Webex-Calling), Configure locations. Checked 2026-09-24.
[^5]: Cisco says all customers should deploy at least the basic emergency calling configuration, which requires at least one customer-owned +E.164 number assigned to each location. Source: [Design to migrate from Unified CM to Webex Calling](https://help.webex.com/en-us/article/nqojzwt/Design-to-migrate-from-Unified-CM-to-Webex-Calling), Emergency calling section. Checked 2026-09-24.
[^6]: Without enhanced emergency calling, Webex Calling relies on telephone-number-based location detection, deriving location from the caller ID asserted on the emergency call. Source: [Enhanced emergency calling for Webex Calling](https://help.webex.com/en-us/article/av6oo3/Enhanced-emergency-calling-for-Webex-Calling), Default emergency calling behaviour. Checked 2026-09-24.
[^7]: A certificate-based Local Gateway trunk supports more than 250 concurrent calls, works with CUBE and listed third-party SBCs, needs a domain claim and a public DNS A or SRV record for the FQDN, and requires CUBE on IOS XE 17.9.1a or later. Source: [Get started with Local Gateway](https://help.webex.com/en-us/article/t9xctu/Get-started-with-Local-Gateway), Trunk type comparison; Supported platforms. Checked 2026-09-24.
[^8]: When the Local Gateway and the PSTN gateway are on the same device, Unified CM needs two trunks to it, using different SIP listening ports, so it can tell calls from Webex from calls from the PSTN and give each a different class of service. Source: [Configure Unified CM for Webex Calling](https://help.webex.com/en-us/article/nqqzbk7/Configure-Unified-CM-for-Webex-Calling), Configure SIP Trunk Security Profile for Trunk to Local Gateway. Checked 2026-09-24.
[^9]: Cisco's Unified CM configuration gives calls from Webex a calling search space containing the DN (+E.164 directory numbers), ESN (abbreviated inter-site dialing), PSTNInternational and onNetRemote partitions. Source: [Configure Unified CM for Webex Calling](https://help.webex.com/en-us/article/nqqzbk7/Configure-Unified-CM-for-Webex-Calling), Create a Calling Search Space for Calls From Webex. Checked 2026-09-24.
[^10]: Control Hub deletes phone numbers in bulk only when they are unassigned; a number assigned to a user, workspace or feature cannot be deleted. Source: [Manage phone numbers in Control Hub](https://help.webex.com/en-us/article/wkj3f0/Manage-phone-numbers-in-Control-Hub), Delete phone numbers in bulk; Delete a phone number. Checked 2026-09-24.
[^11]: A Webex Calling dial plan is configured once for the whole enterprise, holds dial patterns for on-premises destinations (ESN/on-net numbers, +E.164 patterns, SIP URI domains) with wildcards ! and X, and names a trunk or route group as its routing choice. Source: [Configure trunks, route groups, and dial plans for Webex Calling](https://help.webex.com/en-us/article/n0xb944/Configure-trunks,-route-groups,-and-dial-plans-for-Webex-Calling), Dial plan overview. Checked 2026-09-24.
[^12]: The Webex Calling enterprise dial plans used for coexistence contain only the patterns needed to route calls to on-premises destinations. Source: [Implement the migration from Unified CM to Webex Calling](https://help.webex.com/en-us/article/q0pgpb/Implement-the-migration-from-Unified-CM-to-Webex-Calling), Integration with on-premises call control. Checked 2026-09-24.
[^13]: Cisco's implementation guidance says to enable dual-identity and P-Charge-Info support on every PSTN trunk. Source: [Implement the migration from Unified CM to Webex Calling](https://help.webex.com/en-us/article/q0pgpb/Implement-the-migration-from-Unified-CM-to-Webex-Calling), Integration with on-premises call control. Checked 2026-09-24.
[^14]: With enhanced emergency calling enabled at a Local Gateway location, emergency calls go to the E911 service instead of the Local Gateway. Source: [Enhanced emergency calling for Webex Calling](https://help.webex.com/en-us/article/av6oo3/Enhanced-emergency-calling-for-Webex-Calling), PSTN types: local gateway. Checked 2026-09-24.
[^15]: Webex Calling enhanced emergency calling (RedSky) is available in the US, its territories and Canada; locations elsewhere continue to send emergency calls to the PSTN. Source: [Enhanced emergency calling for Webex Calling](https://help.webex.com/en-us/article/av6oo3/Enhanced-emergency-calling-for-Webex-Calling), Countries supported. Checked 2026-09-24.
[^16]: A Webex Calling user's emergency callback number can be their own telephone number, the location's default ECBN, or another assigned number from the user's location; for extension-only users the own-number option does not appear. Source: [Emergency callback number in Control Hub](https://help.webex.com/en-us/article/nzqvtyq/Emergency-callback-number-in-Control-Hub), ECBN options; users without a telephone number. Checked 2026-09-24.
[^17]: Endpoints must be migrated to Webex before the Unified CM servers are decommissioned. Source: [Prepare to migrate from Unified CM to Webex Calling](https://help.webex.com/article/4yz2zd/Prepare-to-migrate-from-Unified-CM-to-Webex-Calling), Video endpoints. Checked 2026-09-24.
[^18]: Cisco says to enable 'Allow extension dialing between locations' only if all extensions within the organization are unique. Source: [Design to migrate from Unified CM to Webex Calling](https://help.webex.com/en-us/article/nqojzwt/Design-to-migrate-from-Unified-CM-to-Webex-Calling), Dial plan section, Webex Calling dial plan. Checked 2026-09-24.
[^19]: Webex Calling extension length is one fixed organization-wide setting of 2 to 10 digits, so all extensions in the deployment have the same length. Source: [Design to migrate from Unified CM to Webex Calling](https://help.webex.com/en-us/article/nqojzwt/Design-to-migrate-from-Unified-CM-to-Webex-Calling), Dial plan section, Webex Calling dial plan. Checked 2026-09-24.
[^20]: Numbers can be added to a Webex Calling location as inactive when they should not yet be included in call routing. Source: [Implement the migration from Unified CM to Webex Calling](https://help.webex.com/en-us/article/q0pgpb/Implement-the-migration-from-Unified-CM-to-Webex-Calling), Configure locations. Checked 2026-09-24.
[^21]: An inactive number assigned to a user, workspace or feature stays inactive until it is activated; Control Hub can activate numbers individually or 500 at a time in bulk. Source: [Manage phone numbers in Control Hub](https://help.webex.com/en-us/article/wkj3f0/Manage-phone-numbers-in-Control-Hub), Activate, modify, or remove phone numbers; Activate numbers in bulk. Checked 2026-09-24.
[^22]: Cisco recommends Cisco IOS XE 17.12.2 or later for both registration-based and certificate-based Local Gateway trunks. Source: [Configure Local Gateway on Cisco IOS XE for Webex Calling](https://help.webex.com/en-us/article/jr1i3r/Configure-Local-Gateway-on-Cisco-IOS-XE-for-Webex-Calling), Prerequisites. Checked 2026-09-24.
[^23]: During a Unified CM to Webex Calling migration, calls between on-premises users and Webex Calling users use the Local Gateway connection. Source: [Design to migrate from Unified CM to Webex Calling](https://help.webex.com/en-us/article/nqojzwt/Design-to-migrate-from-Unified-CM-to-Webex-Calling), PSTN section. Checked 2026-09-24.
[^24]: Cisco's Local Gateway configuration guide assumes a dedicated platform with no existing voice configuration; if an existing PSTN gateway or CUBE Enterprise is reused, the changes must not interrupt existing call flows. Source: [Configure Local Gateway on Cisco IOS XE for Webex Calling](https://help.webex.com/en-us/article/jr1i3r/Configure-Local-Gateway-on-Cisco-IOS-XE-for-Webex-Calling), Introduction / before you begin. Checked 2026-09-24.
[^25]: Cisco says the connection between on-premises and Webex Calling must be designed and sized for the expected number of concurrent calls and the required redundancy. Source: [Design to migrate from Unified CM to Webex Calling](https://help.webex.com/en-us/article/nqojzwt/Design-to-migrate-from-Unified-CM-to-Webex-Calling), PSTN section. Checked 2026-09-24.
[^26]: The trunk between the Local Gateway and the Webex cloud uses SIP over TLS, and media between them uses SRTP. Source: [Configure Local Gateway on Cisco IOS XE for Webex Calling](https://help.webex.com/en-us/article/jr1i3r/Configure-Local-Gateway-on-Cisco-IOS-XE-for-Webex-Calling), Configure Local Gateway: TLS and SRTP. Checked 2026-09-24.
[^27]: A Webex Calling location must have a main number if it has any trunks or any extension-only users, workspaces, virtual lines or features. Source: [Manage phone numbers in Control Hub](https://help.webex.com/en-us/article/wkj3f0/Manage-phone-numbers-in-Control-Hub), Change the phone number for a location. Checked 2026-09-24.
[^28]: Cisco recommends migrating whole physical sites or departments in the same batch, after verifying that the batch's users and telephone numbers are all in Control Hub. Source: [Implement the migration from Unified CM to Webex Calling](https://help.webex.com/en-us/article/q0pgpb/Implement-the-migration-from-Unified-CM-to-Webex-Calling), Migrate users in batches. Checked 2026-09-24.
[^29]: Cisco recommends starting with the Control Hub Migration Insights tool, which analyses Unified CM TAR exports and CDR data to report device eligibility, feature usage, shared lines and hunt groups. Source: [Prepare to migrate from Unified CM to Webex Calling](https://help.webex.com/article/4yz2zd/Prepare-to-migrate-from-Unified-CM-to-Webex-Calling), Migration Insights. Checked 2026-09-24.
[^30]: US MLTS rules require that a user can dial 911 directly from any station without any additional digit, code, prefix or post-fix. Source: [47 CFR § 9.16 - General obligations for MLTS (Cornell LII republication)](https://www.law.cornell.edu/cfr/text/47/9.16), 47 CFR 9.16(a)(1). Checked 2026-09-24.
[^31]: US MLTS rules require automated dispatchable location from on-premises fixed phones (from 6 January 2021) and, for non-fixed and off-premises devices, automated dispatchable location where technically feasible or else a manually updated one (from 6 January 2022). Source: [47 CFR § 9.16 - General obligations for MLTS (Cornell LII republication)](https://www.law.cornell.edu/cfr/text/47/9.16), 47 CFR 9.16(b)(3)(i)-(iii). Checked 2026-09-24.
[^32]: US MLTS rules require the system to send a notification to a central location at the facility, or to another person or organization, when 911 is called. Source: [47 CFR § 9.16 - General obligations for MLTS (Cornell LII republication)](https://www.law.cornell.edu/cfr/text/47/9.16), 47 CFR 9.16(b)(2). Checked 2026-09-24.
[^33]: Cisco recommends moving users in groups and keeping users with dependencies (BLF monitoring, hunt groups, shared lines, call pickup groups) in the same group. Source: [Prepare to migrate from Unified CM to Webex Calling](https://help.webex.com/article/4yz2zd/Prepare-to-migrate-from-Unified-CM-to-Webex-Calling), Migration approach. Checked 2026-09-24.
[^34]: Webex Calling does not support running both CME and the Local Gateway on a single vCUBE instance. Source: [Get started with Local Gateway](https://help.webex.com/en-us/article/t9xctu/Get-started-with-Local-Gateway), Deployment limitations. Checked 2026-09-24.
[^35]: Cisco's phone migration article documents no procedure for returning a migrated phone to Unified CM, so reversal should be treated as unplanned work rather than a supported undo (inferred). Source: [Migrate your phone to Webex Calling](https://help.webex.com/en-us/article/n19c71/Migrate-your-phone-to-Webex-Calling), Whole article (absence of a rollback section). Checked 2026-09-24.
[^36]: Webex Calling voicemail is built in and cannot integrate with premises voicemail such as Unity Connection. Source: [Prepare to migrate from Unified CM to Webex Calling](https://help.webex.com/article/4yz2zd/Prepare-to-migrate-from-Unified-CM-to-Webex-Calling), Voicemail. Checked 2026-09-24.
[^37]: There is no native way to migrate existing Unity Connection voicemail messages or greetings to Webex Calling. Source: [Prepare to migrate from Unified CM to Webex Calling](https://help.webex.com/article/4yz2zd/Prepare-to-migrate-from-Unified-CM-to-Webex-Calling), Voicemail. Checked 2026-09-24.
[^38]: A Control Hub location can be assigned only one PSTN option: Cisco Calling Plans, Cloud Connected PSTN, or premises-based PSTN through a Local Gateway. Source: [Prepare to migrate from Unified CM to Webex Calling](https://help.webex.com/article/4yz2zd/Prepare-to-migrate-from-Unified-CM-to-Webex-Calling), PSTN section. Checked 2026-09-24.
[^39]: For on-premises PSTN and Cloud Connected PSTN, numbers are ordered and ported with the provider before they are configured in Control Hub; for Cisco Calling Plans, ordering and porting start in Control Hub once the location exists. Source: [Implement the migration from Unified CM to Webex Calling](https://help.webex.com/en-us/article/q0pgpb/Implement-the-migration-from-Unified-CM-to-Webex-Calling), Procure PSTN. Checked 2026-09-24.
[^40]: Migrating PSTN per location brings number-porting challenges: coordinating port orders precisely, possible delays, and provider caps on the number of concurrent port requests. Source: [Design to migrate from Unified CM to Webex Calling](https://help.webex.com/en-us/article/nqojzwt/Design-to-migrate-from-Unified-CM-to-Webex-Calling), PSTN section, PSTN strategy. Checked 2026-09-24.
[^41]: Unified CM phones must be on firmware 14.1 or later before Control Hub can migrate them to Webex Calling. Source: [Migrate your phone to Webex Calling](https://help.webex.com/en-us/article/n19c71/Migrate-your-phone-to-Webex-Calling), Prerequisites. Checked 2026-09-24.
[^42]: Control Hub phone migration completes either automatically (wired phones pointed at a chosen TFTP server) or manually by uploading generated BAT files to Unified CM Bulk Administration. Source: [Migrate your phone to Webex Calling](https://help.webex.com/en-us/article/n19c71/Migrate-your-phone-to-Webex-Calling), Complete the migration. Checked 2026-09-24.
[^43]: In Cisco's Local Gateway with Unified CM configuration, calls from Unified CM arriving on port 5060 go to the PSTN and calls arriving on port 5065 go to Webex Calling. Source: [Configure Local Gateway on Cisco IOS XE for Webex Calling](https://help.webex.com/en-us/article/jr1i3r/Configure-Local-Gateway-on-Cisco-IOS-XE-for-Webex-Calling), Local Gateway with Unified CM deployment. Checked 2026-09-24.
[^44]: Cisco describes two PSTN strategies for the transition: move to a Cloud Connected PSTN provider at the start, or keep on-premises PSTN throughout and migrate PSTN location by location. Source: [Design to migrate from Unified CM to Webex Calling](https://help.webex.com/en-us/article/nqojzwt/Design-to-migrate-from-Unified-CM-to-Webex-Calling), PSTN section, PSTN strategy. Checked 2026-09-24.
[^45]: A registration-based Local Gateway trunk supports up to 250 concurrent calls, works only with CUBE, uses digest authentication with a shared username and password, needs no public DNS configuration, and requires CUBE on IOS XE 17.6.1a or later. Source: [Get started with Local Gateway](https://help.webex.com/en-us/article/t9xctu/Get-started-with-Local-Gateway), Trunk type comparison; Supported platforms. Checked 2026-09-24.
[^46]: Cisco strongly recommends always selecting a route group, not a single trunk, as a location's PSTN choice, and says a trunk and a route group must be created for each local gateway. Source: [Implement the migration from Unified CM to Webex Calling](https://help.webex.com/en-us/article/q0pgpb/Implement-the-migration-from-Unified-CM-to-Webex-Calling), Integration with on-premises call control; Configure locations. Checked 2026-09-24.
[^47]: A Webex Calling route group holds between 1 and 10 trunks, and calls are distributed randomly among trunks of the same priority. Source: [Configure trunks, route groups, and dial plans for Webex Calling](https://help.webex.com/en-us/article/n0xb944/Configure-trunks,-route-groups,-and-dial-plans-for-Webex-Calling), Route group: Add a route group for your location. Checked 2026-09-24.
[^48]: The calling party number in the SIP INVITE from the on-premises system must match an E.164 number configured in the Webex Calling route list. Source: [PSTN trunking for hybrid Webex Calling deployments](https://help.webex.com/en-us/article/x3f0tm/PSTN-trunking-for-hybrid-Webex-Calling-deployments), Prerequisites. Checked 2026-09-24.
[^49]: If RedSky is enabled for a route list's location, emergency calls from that route list go through RedSky; otherwise they go through the location's PSTN provider. Source: [PSTN trunking for hybrid Webex Calling deployments](https://help.webex.com/en-us/article/x3f0tm/PSTN-trunking-for-hybrid-Webex-Calling-deployments), Emergency calls. Checked 2026-09-24.
[^50]: With Webex Calling route lists, an inbound PSTN call goes to a trunk in the route list's route group when the called number is in the route list, and an outbound call from the on-premises PBX uses the location's PSTN when its calling number is in the route list. Source: [PSTN trunking for hybrid Webex Calling deployments](https://help.webex.com/en-us/article/x3f0tm/PSTN-trunking-for-hybrid-Webex-Calling-deployments), How it works: call flows. Checked 2026-09-24.
[^51]: Route-list off-net calls need an add-on Route List Calls license that allows 20% bursting over the licensed volume; beyond that, non-emergency calls are blocked. Source: [PSTN trunking for hybrid Webex Calling deployments](https://help.webex.com/en-us/article/x3f0tm/PSTN-trunking-for-hybrid-Webex-Calling-deployments), License limits and bursting. Checked 2026-09-24.
[^52]: Route lists for hybrid PSTN trunking support Cloud Connected Partner PSTN and on-premises PSTN through a Local Gateway. Source: [PSTN trunking for hybrid Webex Calling deployments](https://help.webex.com/en-us/article/x3f0tm/PSTN-trunking-for-hybrid-Webex-Calling-deployments), Supported PSTN types. Checked 2026-09-24.
[^53]: Abbreviated inter-site dialing in Webex Calling uses a location routing prefix (length and steering digit set organization-wide) with a unique site code configured per location. Source: [Design to migrate from Unified CM to Webex Calling](https://help.webex.com/en-us/article/nqojzwt/Design-to-migrate-from-Unified-CM-to-Webex-Calling), Dial plan section, Webex Calling dial plan. Checked 2026-09-24.
[^54]: Seven-digit dial strings on a Webex Calling device using the US dial plan overlap with seven-digit local PSTN dialing; Cisco suggests adding a padding digit to the numbering schema. Source: [Design to migrate from Unified CM to Webex Calling](https://help.webex.com/en-us/article/nqojzwt/Design-to-migrate-from-Unified-CM-to-Webex-Calling), Dial plan section, overlapping dial strings. Checked 2026-09-24.
[^55]: During coexistence, users still on Unified CM keep whatever emergency routing Unified CM already gives them unless their numbers are placed on a Webex Calling route list, so a phased migration runs two emergency-calling paths that each need their own testing (inferred). Source: [PSTN trunking for hybrid Webex Calling deployments](https://help.webex.com/en-us/article/x3f0tm/PSTN-trunking-for-hybrid-Webex-Calling-deployments), Emergency calls; How it works. Checked 2026-09-24.
[^56]: The Control Hub Unified CM migration tool moves users, devices, numbers and locations, up to 1000 users and 1000 devices per task, and needs all end users already provisioned as Webex users. Source: [Migrate Unified CM data to Webex Calling](https://help.webex.com/en-us/article/x974bd/Migrate-Unified-CM-to-Webex), Overview; Prerequisites; Limitations. Checked 2026-09-24.
[^57]: A Webex Calling trunk can be deleted only when it is not in use. Source: [Configure trunks, route groups, and dial plans for Webex Calling](https://help.webex.com/en-us/article/n0xb944/Configure-trunks,-route-groups,-and-dial-plans-for-Webex-Calling), Trunk section, delete a trunk. Checked 2026-09-24.
[^58]: Control Hub shows each trunk's status as online, offline, unknown or impaired under Calling > Call Routing > Trunk; online means every Webex Calling Edge proxy connected to the Local Gateway, and status refreshes every 3 minutes. Source: [Configure trunks, route groups, and dial plans for Webex Calling](https://help.webex.com/en-us/article/n0xb944/Configure-trunks,-route-groups,-and-dial-plans-for-Webex-Calling), Trunk status. Checked 2026-09-24.
[^59]: Cisco's implementation sequence begins by setting up the trunks and local gateways that interconnect with the on-premises call control system, then creating enterprise dial plans that point to the appropriate route group. Source: [Implement the migration from Unified CM to Webex Calling](https://help.webex.com/en-us/article/q0pgpb/Implement-the-migration-from-Unified-CM-to-Webex-Calling), Integration with on-premises call control. Checked 2026-09-24.
[^60]: Cisco's design provisions two DIDs per Webex Calling location: one main number (for example for an auto attendant) and one for the voicemail portal. Source: [Design to migrate from Unified CM to Webex Calling](https://help.webex.com/en-us/article/nqojzwt/Design-to-migrate-from-Unified-CM-to-Webex-Calling), Location design section. Checked 2026-09-24.
[^61]: After a transition, Cisco says to disable or delete the user and device directory numbers and calling features on Unified CM. Source: [Implement the migration from Unified CM to Webex Calling](https://help.webex.com/en-us/article/q0pgpb/Implement-the-migration-from-Unified-CM-to-Webex-Calling), Post-migration cleanup. Checked 2026-09-24.
[^62]: For coexistence the Unified CM dial plan must support +E.164 dialing, extension dialing (intra-site and inter-site), abbreviated inter-site dialing and forced on-net dialing to Webex Calling. Source: [Design to migrate from Unified CM to Webex Calling](https://help.webex.com/en-us/article/nqojzwt/Design-to-migrate-from-Unified-CM-to-Webex-Calling), Dial plan section, Unified CM dial plan changes. Checked 2026-09-24.
[^63]: On Unified CM, Cisco configures full +E.164 route patterns for the DID ranges in Webex, pointing to a Webex route list whose route group contains the SIP trunk to the Local Gateway. Source: [Configure Unified CM for Webex Calling](https://help.webex.com/en-us/article/nqqzbk7/Configure-Unified-CM-for-Webex-Calling), Configure Route Group for Webex; Configure Route List for Webex; Configure Route Patterns for Webex Destinations. Checked 2026-09-24.
[^64]: Calls to On-Premises Extensions is enabled per location: calls from that location to an unknown 2-10 digit extension go to the selected route group or trunk, bounded by a Maximum Unknown Extension Length. Source: [Configure trunks, route groups, and dial plans for Webex Calling](https://help.webex.com/en-us/article/n0xb944/Configure-trunks,-route-groups,-and-dial-plans-for-Webex-Calling), Configure calls to on-premises extensions; Configure call routing between Webex Calling and premises. Checked 2026-09-24.
[^65]: All users, whether or not they have moved calling platform yet, should be provisioned in Webex at or before the start of the project, which also enables directory search across migrated and non-migrated users. Source: [Prepare to migrate from Unified CM to Webex Calling](https://help.webex.com/article/4yz2zd/Prepare-to-migrate-from-Unified-CM-to-Webex-Calling), Prerequisites: user provisioning. Checked 2026-09-24.
[^66]: Each Webex Calling location needs its voicemail pilot number (voice portal number) set during location configuration. Source: [Implement the migration from Unified CM to Webex Calling](https://help.webex.com/en-us/article/q0pgpb/Implement-the-migration-from-Unified-CM-to-Webex-Calling), Configure locations. Checked 2026-09-24.
[^67]: Acceptance testing includes confirming voicemail boxes are correctly assigned and accessible both from within the organization and remotely. Source: [Implement the migration from Unified CM to Webex Calling](https://help.webex.com/en-us/article/q0pgpb/Implement-the-migration-from-Unified-CM-to-Webex-Calling), Acceptance testing. Checked 2026-09-24.
[^68]: Cisco's design puts +E.164 route patterns for all Webex Calling destinations into a dedicated Webex Calling partition on Unified CM. Source: [Design to migrate from Unified CM to Webex Calling](https://help.webex.com/en-us/article/nqojzwt/Design-to-migrate-from-Unified-CM-to-Webex-Calling), Dial plan section, routing to Webex Calling. Checked 2026-09-24.
[^69]: The Unified CM partition holding Webex destinations must be added to every calling search space that needs to reach Webex, including the calling search space of the inbound PSTN trunk. Source: [Configure Unified CM for Webex Calling](https://help.webex.com/en-us/article/nqqzbk7/Configure-Unified-CM-for-Webex-Calling), Create a Partition for Webex Destinations. Checked 2026-09-24.
[^70]: Cisco describes the coexistence phase of a Unified CM to Webex Calling migration as one in which some users, devices and soft clients have moved to Webex Calling while others remain on on-premises Unified CM call control. Source: [Introduction (Migrate Unified CM to Webex Calling)](https://help.webex.com/en-us/article/nbedetf/Introduction), Introduction > Migration approach. Checked 2026-09-24.
[^71]: Cisco describes retaining on-premises PSTN throughout the transition, with PSTN migrated per location as users move, as one option; Webex Calling users then use on-premises PSTN through the Local Gateway connection. Source: [Design to migrate from Unified CM to Webex Calling](https://help.webex.com/en-us/article/nqojzwt/Design-to-migrate-from-Unified-CM-to-Webex-Calling), Design to migrate > PSTN. Checked 2026-09-24.
[^72]: For dual call control, Cisco says to deploy one or more Local Gateways for on-premises PSTN to allow calling between Webex Calling and Unified CM endpoints. Source: [Implement the migration from Unified CM to Webex Calling](https://help.webex.com/en-us/article/q0pgpb/Implement-the-migration-from-Unified-CM-to-Webex-Calling), Implement the migration > Integration with on-premises call control. Checked 2026-09-24.
[^73]: Cisco says one-way latency between the Local Gateway and the Webex Calling access SBC should not exceed 100 ms. Source: [Prepare to migrate from Unified CM to Webex Calling](https://help.webex.com/en-us/article/4yz2zd/Prepare-to-migrate-from-Unified-CM-to-Webex-Calling), Prepare to migrate > PSTN connectivity. Checked 2026-09-24.
[^74]: PID A-FLEX-P-CALL provides temporary licensing for up to 18 months during the transition, with basic-level support on both calling environments. Source: [Migrate Unified CM data to Webex Calling](https://help.webex.com/en-us/article/x974bd/Migrate-Unified-CM-to-Webex), Migrate Unified CM data to Webex Calling > Before you begin. Checked 2026-09-24.
[^75]: Cisco recommends moving users together when they depend on each other through BLF monitoring, the same hunt pilot or group, shared lines, the same pickup group, shared call-park numbers, intercom or admin/exec relationships. Source: [Prepare to migrate from Unified CM to Webex Calling](https://help.webex.com/en-us/article/4yz2zd/Prepare-to-migrate-from-Unified-CM-to-Webex-Calling), Prepare to migrate > Users. Checked 2026-09-24.
[^76]: Cisco says the connection between on-premises and Webex Calling must be designed and sized for the expected number of concurrent calls and the required redundancy. Source: [Design to migrate from Unified CM to Webex Calling](https://help.webex.com/en-us/article/nqojzwt/Design-to-migrate-from-Unified-CM-to-Webex-Calling), Design to migrate from Unified CM to Webex Calling > PSTN. Checked 2026-09-24.
[^77]: A Control Hub location can be assigned only one PSTN option: Cisco Calling Plans, Cloud Connect, or on-premises PSTN via Local Gateway. Source: [Prepare to migrate from Unified CM to Webex Calling](https://help.webex.com/en-us/article/4yz2zd/Prepare-to-migrate-from-Unified-CM-to-Webex-Calling), Prepare to migrate > PSTN connectivity. Checked 2026-09-24.
[^78]: Cisco says users moved to Webex Calling can search the Webex directory for enterprise users still on Jabber or Unified CM. Source: [Prepare to migrate from Unified CM to Webex Calling](https://help.webex.com/en-us/article/4yz2zd/Prepare-to-migrate-from-Unified-CM-to-Webex-Calling), Prepare to migrate > Users. Checked 2026-09-24.
[^79]: Cisco's example calling search space for calls arriving from Webex includes partitions for +E.164 directory numbers (DN), abbreviated inter-site dialing (ESN) and PSTN access (PSTNInternational). Source: [Configure Unified CM for Webex Calling](https://help.webex.com/en-us/article/nqqzbk7/Configure-Unified-CM-for-Webex-Calling), Create a Calling Search Space for Calls From Webex. Checked 2026-09-24.
[^80]: To avoid call loops, the inbound calling search space on the Unified CM trunk from the Local Gateway must not have access to the Webex Calling partition. Source: [Design to migrate from Unified CM to Webex Calling](https://help.webex.com/en-us/article/nqojzwt/Design-to-migrate-from-Unified-CM-to-Webex-Calling), Design to migrate > On-premises dial plan in Unified CM. Checked 2026-09-24.
[^81]: Cisco's coexistence design adds a Webex Calling partition to the Unified CM dial plan containing +E.164 route patterns for all Webex Calling destinations. Source: [Design to migrate from Unified CM to Webex Calling](https://help.webex.com/en-us/article/nqojzwt/Design-to-migrate-from-Unified-CM-to-Webex-Calling), Design to migrate > On-premises dial plan in Unified CM. Checked 2026-09-24.
[^82]: During the transition the Unified CM dial plan must support +E.164 dialing to Webex Calling and extension dialing to Webex Calling, intra-site and also inter-site when extension ranges are unique. Source: [Design to migrate from Unified CM to Webex Calling](https://help.webex.com/en-us/article/nqojzwt/Design-to-migrate-from-Unified-CM-to-Webex-Calling), Design to migrate > On-premises dial plan in Unified CM (bulleted list of transition requirements). Checked 2026-09-24.
[^83]: Cisco's Unified CM configuration adds abbreviated inter-site dialing normalization for Webex destinations, translating enterprise numbers to +E.164 before routing to the Webex partition. Source: [Configure Unified CM for Webex Calling](https://help.webex.com/en-us/article/nqqzbk7/Configure-Unified-CM-for-Webex-Calling), Configure Abbreviated Intersite Dialing Normalization for Webex. Checked 2026-09-24.
[^84]: Unified CM best-match routing means a +E.164 directory number still provisioned on Unified CM wins over a wildcarded +E.164 route pattern pointing to Webex Calling, so calls to that number stay on Unified CM. Source: [Design to migrate from Unified CM to Webex Calling](https://help.webex.com/en-us/article/nqojzwt/Design-to-migrate-from-Unified-CM-to-Webex-Calling), Design to migrate > On-premises dial plan in Unified CM (best match paragraph). Checked 2026-09-24.
[^85]: Webex Calling internal extension length can be set from 2 to 10 digits, with a default of 4. Source: [Configure your Webex Calling dial plan](https://help.webex.com/en-us/article/pxtu15/Configure-your-Webex-Calling-dial-plan), Configure your Webex Calling dial plan > Internal Extension Length. Checked 2026-09-24.
[^86]: In Cisco's migration design, all site codes of all locations must be unique and have the same length. Source: [Design to migrate from Unified CM to Webex Calling](https://help.webex.com/en-us/article/nqojzwt/Design-to-migrate-from-Unified-CM-to-Webex-Calling), Design to migrate > Locations. Checked 2026-09-24.
[^87]: In Cisco's migration design, no extension range may start with the inter-site steering digit or the PSTN steering digit. Source: [Design to migrate from Unified CM to Webex Calling](https://help.webex.com/en-us/article/nqojzwt/Design-to-migrate-from-Unified-CM-to-Webex-Calling), Design to migrate > Webex Calling dial plan. Checked 2026-09-24.
[^88]: Webex Calling's 'Allow extension dialing between locations' toggle should be enabled only when the organization has no duplicate extensions across its locations. Source: [Configure your Webex Calling dial plan](https://help.webex.com/en-us/article/pxtu15/Configure-your-Webex-Calling-dial-plan), Configure your Webex Calling dial plan > Internal dialing. Checked 2026-09-24.
[^89]: If extension ranges overlap across sites, Cisco says an enterprise numbering plan must be created by prefixing extensions with an access code and a site code. Source: [Design to migrate from Unified CM to Webex Calling](https://help.webex.com/en-us/article/nqojzwt/Design-to-migrate-from-Unified-CM-to-Webex-Calling), Design to migrate > Webex Calling dial plan. Checked 2026-09-24.
[^90]: Webex Calling dial plan patterns may be +E.164 patterns, enterprise dial patterns without a leading plus, or SIP URI domain patterns; wildcards X and ! are supported but cannot be combined in one pattern. Source: [Configure trunks, route groups, and dial plans for Webex Calling](https://help.webex.com/article/n0xb944/Configure-Trunks-Route-Groups-and-Dial-Plans-for-Cisco-Webex-Calling), Configure trunks, route groups, and dial plans > Dial plans > dial patterns. Checked 2026-09-24.
[^91]: For unknown-extension handling, Standard Behavior is the default and recommended option for PBX interoperability, while Legacy Behavior exists for backward compatibility and is not recommended when dial plans are configured. Source: [Configure trunks, route groups, and dial plans for Webex Calling](https://help.webex.com/article/n0xb944/Configure-Trunks-Route-Groups-and-Dial-Plans-for-Cisco-Webex-Calling), Configure trunks, route groups, and dial plans > Calls to On-Premises Extensions. Checked 2026-09-24.
[^92]: In the reverse direction the transition dial plan must support forced on-net dialing and inter-site extension dialing from Webex Calling to Unified CM. Source: [Design to migrate from Unified CM to Webex Calling](https://help.webex.com/en-us/article/nqojzwt/Design-to-migrate-from-Unified-CM-to-Webex-Calling), Design to migrate > On-premises dial plan in Unified CM (bulleted list of transition requirements). Checked 2026-09-24.
[^93]: The Unified CM transition dial plan must support call-back from the missed calls directory to destinations on Webex Calling. Source: [Design to migrate from Unified CM to Webex Calling](https://help.webex.com/en-us/article/nqojzwt/Design-to-migrate-from-Unified-CM-to-Webex-Calling), Design to migrate > On-premises dial plan in Unified CM (bulleted list of transition requirements). Checked 2026-09-24.
[^94]: Cisco lists porting challenges including coordinating port orders precisely, potential delays, and provider limits such as a cap on concurrent port requests. Source: [Design to migrate from Unified CM to Webex Calling](https://help.webex.com/en-us/article/nqojzwt/Design-to-migrate-from-Unified-CM-to-Webex-Calling), Design to migrate > PSTN. Checked 2026-09-24.
[^95]: The transition dial plan must carry PSTN calls from Webex Calling via on-premises PSTN when that is used, and PSTN calls from Unified CM via Webex Calling when PSTN trunking for hybrid deployments is used. Source: [Design to migrate from Unified CM to Webex Calling](https://help.webex.com/en-us/article/nqojzwt/Design-to-migrate-from-Unified-CM-to-Webex-Calling), Design to migrate > On-premises dial plan in Unified CM (bulleted list of transition requirements). Checked 2026-09-24.
[^96]: Webex Calling cannot integrate with a premises-based voicemail system such as Unity Connection or Unity Connection Express. Source: [Prepare to migrate from Unified CM to Webex Calling](https://help.webex.com/en-us/article/4yz2zd/Prepare-to-migrate-from-Unified-CM-to-Webex-Calling), Prepare to migrate > Cisco integrations: Unity Connection UCCX UCCE. Checked 2026-09-24.
[^97]: There is no native way to migrate existing Unity Connection voicemail messages or greetings to Webex Calling voicemail. Source: [Prepare to migrate from Unified CM to Webex Calling](https://help.webex.com/en-us/article/4yz2zd/Prepare-to-migrate-from-Unified-CM-to-Webex-Calling), Prepare to migrate > Cisco integrations: Unity Connection UCCX UCCE. Checked 2026-09-24.
[^98]: Phones on Unified CM that are being migrated must run phone load version 14.1 or later. Source: [Migrate Unified CM data to Webex Calling](https://help.webex.com/en-us/article/x974bd/Migrate-Unified-CM-to-Webex), Migrate Unified CM data to Webex Calling > Before you begin. Checked 2026-09-24.
[^99]: The Control Hub Unified CM migration tool migrates at most 1000 users and 1000 devices per task; larger migrations need multiple tasks. Source: [Migrate Unified CM data to Webex Calling](https://help.webex.com/en-us/article/x974bd/Migrate-Unified-CM-to-Webex), Migrate Unified CM data to Webex Calling > Before you begin. Checked 2026-09-24.
[^100]: The Unified CM export/import migration covers auto attendants, devices, configured lines, device layout including shared lines, virtual lines, call queues, hunt groups, call park and user call forwarding and monitoring. Source: [Migrate devices and features from Unified CM to Webex Calling](https://help.webex.com/en-us/article/d2lemv/Migration-of-Devices-and-Features-From-Cisco-unified-Communications-Manager(UCM)-to-Webex-Calling-Multi-Tenant), Migrate devices and features from Unified CM to Webex Calling > supported features list. Checked 2026-09-24.
[^101]: Cisco's implementation checklist says to disable or delete the user and device directory number and calling features on Unified CM after the user has transitioned to Webex Calling. Source: [Implement the migration from Unified CM to Webex Calling](https://help.webex.com/en-us/article/q0pgpb/Implement-the-migration-from-Unified-CM-to-Webex-Calling), Implement the migration > user batch migration checklist. Checked 2026-09-24.
[^102]: Webex Calling Customer Assist can be deployed for agents while other employees stay on Unified CM, interconnected through Local Gateway; Unified CM clusters must be version 14 or 15 with SUs or later. Source: [Configure Webex Calling Customer Assist for Unified Communications Manager](https://help.webex.com/en-us/article/n8md850/Webex-Calling-Hybrid), Configure Webex Calling Customer Assist for Unified Communications Manager > Customer Assist; requirements. Checked 2026-09-24.