# Microsoft Teams Phone architecture and licensing Canonical: https://warmtransfer.net/knowledge/teams-phone-architecture Last verified: 2026-09-06 A Teams Phone license and a PSTN solution are separate requirements, where the license grants calling capabilities and the PSTN solution supplies phone numbers alongside domestic, international, and emergency connectivity[^11]. Microsoft states that Teams Phone supports coexistent integrations when an organization maintains another phone system or a contact center[^33]. ## PSTN connectivity architecture Microsoft documents 4 Teams Phone PSTN connectivity models: Microsoft Calling Plan, Operator Connect, Teams Phone Mobile, and Direct Routing[^10]. The Teams Phone PSTN connectivity comparison assigns a Microsoft-managed model to Calling Plan, a shared operator-and-Microsoft model to Operator Connect, a participating-mobile-operator model to Teams Phone Mobile, and a customer-managed Session Border Controller (SBC) model to Direct Routing[^24]. Microsoft directs organizations to choose Teams Phone PSTN connectivity based on management preference, carrier relationships, calling patterns, and existing telephony infrastructure, permitting different models across users, locations, and business requirements[^1]. A single Teams tenant can maintain more than 1 PSTN integration and utilize any supported combination of PSTN solutions[^34]. Direct Routing connects customer telephony infrastructure to Teams Phone through a supported customer-provided SBC[^2]. The Direct Routing plan requires: - A Microsoft-certified SBC[^4] - Telephony trunks[^4] - A Microsoft 365 tenant with online users[^4] - A verified domain[^4] - A public IP address and DNS record for the SBC FQDN[^4] - A public certificate[^4] - Permitted signaling and media paths[^4] A Direct Routing SBC FQDN must belong to a verified Microsoft 365 tenant domain and cannot use the default onmicrosoft.com domain[^6]. Microsoft states that Direct Routing is not supported in Islands mode[^5]. In hybrid estates, Microsoft documents Direct Routing alongside other Teams Phone PSTN models and names third-party PBXs, analog devices, and specialized routing as uses for the Direct Routing leg[^7]. Microsoft's Direct Routing plan sequences infrastructure and licensing prior to SBC selection and connectivity, followed by routing and user assignment, requiring inbound, outbound, emergency, failover, policy, and call-quality validation before production rollout[^3]. Operator Connect utilizes a Microsoft-certified operator to manage PSTN infrastructure, enabling administrators to manage users in the Teams admin center without deploying customer SBCs[^18]. Onboarding users to Operator Connect requires target users to be configured in Teams Only mode[^19]. Operator Connect planning requires a certified provider in each deployment country or region, requiring customer evaluation of country coverage, number availability, and porting support before onboarding[^21]. Microsoft divides support boundaries by assigning Teams services administration and the Operator Connect integration to Microsoft, while assigning PSTN connectivity, number provisioning and porting, calling service, and PSTN troubleshooting to the operator[^20]. ## Licensing and provisioning sequence Each Teams Phone user must receive a Teams Phone license and must also be voice-enabled[^35]. Microsoft's high-level Teams Phone roadmap orders provisioning into licensing, PSTN connectivity, numbers, emergency calling, optional auto attendants, optional call queues, other features, and ongoing management[^31]. However, Microsoft warns that Teams Phone number management and emergency-calling steps and sequence can differ by PSTN connectivity option[^25]. Microsoft describes Shared Calling as an initial phased-migration step that allows large groups to use Teams Phone calling without assigning an individual phone number to every user[^32]. Telephone numbers are not included with Teams Phone licensing and must be acquired from the provider supplying the tenant's PSTN connectivity[^17]. How a tenant acquires and manages these numbers depends on whether it deploys Calling Plan, Operator Connect, Teams Phone Mobile, or Direct Routing[^15]. Teams Phone distinguishes user numbers, voice-application numbers for auto attendants and call queues, and conference numbers for dial-in bridges[^16]. ## Emergency calling policies Teams emergency calling policies apply across Calling Plan, Operator Connect, Teams Phone Mobile, and Direct Routing deployments[^8]. When a Teams user and the network site the user is at both have assigned emergency calling policies, the site's policy overrides the user's policy[^14]. A Teams emergency calling policy can send security-desk chat notifications or conference configured recipients into the emergency call in either muted or unmuted mode[^9]. ## Network infrastructure, branch survivability, and operations Microsoft's network baseline requires site internet access to Microsoft 365 endpoints and a verified Microsoft 365 domain prior to rollout[^12]. Optimization guidance requires external DNS resolution, stable NAT mappings, adequate NAT pool capacity, efficient Microsoft-network egress, VPN bypass for Teams traffic, and QoS across managed network segments[^13]. To assess performance, Microsoft assigns distinct scopes to its monitoring tools: Call Quality Dashboard serves as an organization-wide trend view, whereas the Teams admin center serves as a per-user call and meeting troubleshooting view[^26]. For branch resilience, a Direct Routing Survivable Branch Appliance (SBA) supports local PSTN calling during a Microsoft cloud connectivity outage, provided the branch intranet and SBC remain reachable[^30]. Direct Routing SBA prerequisites require Media Bypass, TLS 1.2, and firewall access for client, SBC, NTP, and Microsoft 365 communication ports[^29]. Under SBA operational mode, web and virtual-machine clients are unsupported, emergency location information is not shared, and Teams Emergency Call Routing Policies are unsupported[^28]. Additionally, Microsoft states that a tenant using Continuous Access Evaluation (CAE) tokens may be limited to about 30 minutes of SBA operation[^27]. For rollout validation, Microsoft's pilot methodology calls for actual users, realistic work scenarios, and validation of technical and user experiences[^23]. During the pilot, Microsoft directs teams to monitor network and usage data, collect feedback, review helpdesk tickets, and assess those results before deciding whether to expand or revisit the plan[^22]. ## See also - See also [Teams Phone Direct Routing and SBC certification](https://warmtransfer.net/knowledge/teams-direct-routing). - See also [Teams Operator Connect and Azure Communication routing](https://warmtransfer.net/knowledge/teams-operator-connect). - See also [Teams emergency calling and location policies](https://warmtransfer.net/knowledge/teams-emergency-calling). - See also [Teams call quality dashboard and analytics](https://warmtransfer.net/knowledge/teams-call-analytics). - See also [Teams contact center integration models](https://warmtransfer.net/knowledge/teams-contact-center-integration). - See also [Identity SSO and directory provisioning for UC](https://warmtransfer.net/knowledge/identity-sso-provisioning). - See also [Webex Calling architecture and deployment models](https://warmtransfer.net/knowledge/webex-calling-architecture). - See also [Teams voice routing policies and dial plans](https://warmtransfer.net/knowledge/teams-voice-routing). ## Applicability Applies to: Microsoft Teams Phone. Deployments: cloud, customer-managed-sbc, direct-routing-sba, and operator-managed-pstn. Sources checked 2026-09-06. Operator Connect requires evaluating certified provider availability, which varies by country or region[^21]. ## What remains uncertain The following items are not covered by the sources below: - Defining supported Teams Phone and Webex Contact Center coexistence patterns is not covered by the sources below. - Mapping emergency routing and location duties by country and PSTN model is not covered by the sources below. - Building a provider-specific number port and rollback runbook is not covered by the sources below. - Mapping CUCM and Webex Calling objects to Teams Phone objects is not covered by the sources below. - Determining which Cisco endpoints can be reused with Teams Phone is not covered by the sources below. - Building a dated operator and number coverage inventory by country is not covered by the sources below. - Resolving the supportable CAE design for branches that require SBA is not covered by the sources below. ## Sources [^1]: Microsoft directs organizations to choose Teams Phone PSTN connectivity from their management preference carrier relationship calling patterns and existing telephony infrastructure and permits different models for users locations and business requirements. Source: [PSTN connectivity options](https://learn.microsoft.com/en-us/microsoftteams/pstn-connectivity), PSTN connectivity options and Use more than one PSTN connectivity type. Checked 2026-09-06. [^2]: Direct Routing connects customer telephony infrastructure to Teams Phone through a supported customer-provided Session Border Controller. Source: [Plan Direct Routing](https://learn.microsoft.com/en-us/microsoftteams/direct-routing-plan), Plan Direct Routing, introduction. Checked 2026-09-06. [^3]: Microsoft's Direct Routing plan puts infrastructure and licensing before SBC selection and connectivity then routing and user assignment and requires inbound outbound emergency failover policy and call-quality validation before production rollout. Source: [Plan Direct Routing](https://learn.microsoft.com/en-us/microsoftteams/direct-routing-plan), Deployment overview and Verify your deployment. Checked 2026-09-06. [^4]: The current Direct Routing plan requires a Microsoft-certified SBC telephony trunks a Microsoft 365 tenant with online users a verified domain a public IP address and DNS record for the SBC FQDN a public certificate and permitted signaling and media paths. Source: [Plan Direct Routing](https://learn.microsoft.com/en-us/microsoftteams/direct-routing-plan), Infrastructure requirements table. Checked 2026-09-06. [^5]: Microsoft states that Direct Routing is not supported in Islands mode. Source: [Plan Direct Routing](https://learn.microsoft.com/en-us/microsoftteams/direct-routing-plan), Licensing requirements, note after the list. Checked 2026-09-06. [^6]: A Direct Routing SBC FQDN must belong to a verified Microsoft 365 tenant domain and cannot use the default onmicrosoft.com domain. Source: [Plan Direct Routing](https://learn.microsoft.com/en-us/microsoftteams/direct-routing-plan), SBC domain names. Checked 2026-09-06. [^7]: Microsoft documents Direct Routing alongside other Teams Phone PSTN models and names third-party PBXs analog devices and specialized routing as uses for the Direct Routing leg. Source: [Plan Direct Routing](https://learn.microsoft.com/en-us/microsoftteams/direct-routing-plan), Direct Routing with Calling Plan and Operator Connect. Checked 2026-09-06. [^8]: Teams emergency calling policies apply to Calling Plan Operator Connect Teams Phone Mobile and Direct Routing deployments. Source: [Manage emergency calling policies in Microsoft Teams](https://learn.microsoft.com/en-us/microsoftteams/manage-emergency-calling-policies), Manage emergency calling policies, opening paragraph. Checked 2026-09-06. [^9]: A Teams emergency calling policy can send security-desk chat notifications or conference configured recipients into the emergency call in muted or unmuted mode. Source: [Manage emergency calling policies in Microsoft Teams](https://learn.microsoft.com/en-us/microsoftteams/manage-emergency-calling-policies), Create a custom emergency calling policy, notification mode. Checked 2026-09-06. [^10]: Microsoft documents four Teams Phone PSTN connectivity models: Microsoft Calling Plan Operator Connect Teams Phone Mobile and Direct Routing. Source: [PSTN connectivity options](https://learn.microsoft.com/en-us/microsoftteams/pstn-connectivity), PSTN connectivity options, highlights and comparison table. Checked 2026-09-06. [^11]: A Teams Phone license and a PSTN solution are separate requirements: the license grants the calling capabilities while the PSTN solution supplies phone numbers and domestic international and emergency connectivity. Source: [What is Teams Phone](https://learn.microsoft.com/en-us/microsoftteams/what-is-phone-system-in-office-365), What is Teams Phone, add-on options and note after the list. Checked 2026-09-06. [^12]: Microsoft's Teams network baseline requires site internet access to Microsoft 365 endpoints and a verified Microsoft 365 domain before rollout. Source: [Prepare your organization's network for Microsoft Teams](https://learn.microsoft.com/en-us/microsoftteams/prepare-network), Network requirements, checks 1 and 2. Checked 2026-09-06. [^13]: Microsoft's Teams network guidance calls for external DNS resolution stable NAT mappings adequate NAT pool capacity efficient Microsoft-network egress VPN bypass for Teams traffic and QoS across managed network segments. Source: [Prepare your organization's network for Microsoft Teams](https://learn.microsoft.com/en-us/microsoftteams/prepare-network), Network optimization table. Checked 2026-09-06. [^14]: When a Teams user and the network site the user is at both have emergency calling policies the site's policy overrides the user's policy. Source: [Manage emergency calling policies in Microsoft Teams](https://learn.microsoft.com/en-us/microsoftteams/manage-emergency-calling-policies), Manage emergency calling policies, policy assignment overview. Checked 2026-09-06. [^15]: How a tenant acquires and manages Teams Phone numbers depends on whether it uses Calling Plan Operator Connect Teams Phone Mobile or Direct Routing. Source: [Get telephone numbers in Microsoft Teams](https://learn.microsoft.com/en-us/microsoftteams/manage-phone-numbers-landing-page), Acquiring and managing telephone numbers table. Checked 2026-09-06. [^16]: Teams Phone distinguishes user numbers voice-application numbers for auto attendants and call queues and conference numbers for dial-in bridges. Source: [Get telephone numbers in Microsoft Teams](https://learn.microsoft.com/en-us/microsoftteams/manage-phone-numbers-landing-page), Number usage types table. Checked 2026-09-06. [^17]: Telephone numbers are not included with Teams Phone licensing and are acquired from the provider that supplies the tenant's PSTN connectivity. Source: [Get telephone numbers in Microsoft Teams](https://learn.microsoft.com/en-us/microsoftteams/manage-phone-numbers-landing-page), Get telephone numbers, overview. Checked 2026-09-06. [^18]: Operator Connect uses a Microsoft-certified operator to manage the PSTN infrastructure while administrators manage users in Teams admin center without deploying their own SBCs. Source: [Plan for Operator Connect](https://learn.microsoft.com/en-us/microsoftteams/operator-connect-plan), Plan for Operator Connect, introduction. Checked 2026-09-06. [^19]: Operator Connect onboarding requires the target users to be configured in Teams Only mode. Source: [Plan for Operator Connect](https://learn.microsoft.com/en-us/microsoftteams/operator-connect-plan), Onboarding, Step 1: Verify prerequisites. Checked 2026-09-06. [^20]: Microsoft assigns Teams services administration and the Operator Connect integration to Microsoft while assigning PSTN connectivity number provisioning and porting calling service and PSTN troubleshooting to the operator. Source: [Plan for Operator Connect](https://learn.microsoft.com/en-us/microsoftteams/operator-connect-plan), Support boundaries. Checked 2026-09-06. [^21]: Operator Connect planning requires a certified provider in each deployment country or region and asks the customer to evaluate country coverage number availability and porting support before onboarding. Source: [Plan for Operator Connect](https://learn.microsoft.com/en-us/microsoftteams/operator-connect-plan), Onboarding, Steps 1 through 3. Checked 2026-09-06. [^22]: During a Teams pilot Microsoft directs the team to monitor network and usage data collect feedback review helpdesk tickets and assess those results before deciding whether to expand or revisit the plan. Source: [Conduct a user pilot](https://learn.microsoft.com/en-us/microsoftteams/pilot-essentials), Conduct your pilot and Assess learnings and evaluate your go-forward plan. Checked 2026-09-06. [^23]: Microsoft's Teams pilot method calls for actual users realistic work scenarios and validation of both the technical and user experiences. Source: [Conduct a user pilot](https://learn.microsoft.com/en-us/microsoftteams/pilot-essentials), Conduct a user pilot, introduction and Design your test plan. Checked 2026-09-06. [^24]: The Teams Phone PSTN connectivity comparison assigns a Microsoft-managed model to Calling Plan a shared operator-and-Microsoft model to Operator Connect a participating-mobile-operator model to Teams Phone Mobile and a customer-managed SBC model to Direct Routing. Source: [PSTN connectivity options](https://learn.microsoft.com/en-us/microsoftteams/pstn-connectivity), PSTN connectivity types comparison, Management model row. Checked 2026-09-06. [^25]: Microsoft warns that Teams Phone number management and emergency-calling steps and sequence can differ by PSTN connectivity option. Source: [Set up Teams Phone in your organization](https://learn.microsoft.com/en-us/microsoftteams/setting-up-your-phone-system), Provisioning steps, note after overview. Checked 2026-09-06. [^26]: Microsoft describes Call Quality Dashboard as an organization-wide trend view and Teams admin center as a per-user call and meeting troubleshooting view. Source: [Prepare your organization's network for Microsoft Teams](https://learn.microsoft.com/en-us/microsoftteams/prepare-network), Best practice: Monitor your network by using CQD and Teams admin center. Checked 2026-09-06. [^27]: Microsoft states that a tenant using Continuous Access Evaluation tokens may have only about 30 minutes of SBA operation. Source: [Survivable Branch Appliance for Direct Routing](https://learn.microsoft.com/en-us/microsoftteams/direct-routing-survivable-branch-appliance), Known issues and considerations, CAE token bullet. Checked 2026-09-06. [^28]: In SBA mode web and virtual-machine clients are unsupported emergency location information is not shared and Teams Emergency Call Routing Policies are unsupported. Source: [Survivable Branch Appliance for Direct Routing](https://learn.microsoft.com/en-us/microsoftteams/direct-routing-survivable-branch-appliance), How it works and Known issues and considerations. Checked 2026-09-06. [^29]: The Direct Routing SBA requires Media Bypass TLS 1.2 and firewall access for its documented client SBC NTP and Microsoft 365 communication ports. Source: [Survivable Branch Appliance for Direct Routing](https://learn.microsoft.com/en-us/microsoftteams/direct-routing-survivable-branch-appliance), Prerequisites. Checked 2026-09-06. [^30]: A Direct Routing Survivable Branch Appliance supports local PSTN calling during a Microsoft-cloud connectivity outage when the branch intranet and SBC remain reachable. Source: [Survivable Branch Appliance for Direct Routing](https://learn.microsoft.com/en-us/microsoftteams/direct-routing-survivable-branch-appliance), Survivable Branch Appliance, opening scenario. Checked 2026-09-06. [^31]: Microsoft's high-level Teams Phone roadmap orders licensing PSTN connectivity numbers emergency calling optional auto attendants optional call queues other features and ongoing management. Source: [Set up Teams Phone in your organization](https://learn.microsoft.com/en-us/microsoftteams/setting-up-your-phone-system), Provisioning steps, overview of steps. Checked 2026-09-06. [^32]: Microsoft describes Shared Calling as an initial phased-migration step that lets large groups use Teams Phone calling without assigning a phone number to every user. Source: [Set up Teams Phone in your organization](https://learn.microsoft.com/en-us/microsoftteams/setting-up-your-phone-system), Step 2: Choose a PSTN connectivity option, Shared Calling note. Checked 2026-09-06. [^33]: Microsoft states that Teams Phone supports coexistent integrations when an organization has another phone system or a contact center. Source: [What is Teams Phone](https://learn.microsoft.com/en-us/microsoftteams/what-is-phone-system-in-office-365), What is Teams Phone, paragraph after client support. Checked 2026-09-06. [^34]: A Teams tenant can have more than one PSTN integration and can use any supported combination of PSTN solutions. Source: [What is Teams Phone](https://learn.microsoft.com/en-us/microsoftteams/what-is-phone-system-in-office-365), What is Teams Phone, add-on options. Checked 2026-09-06. [^35]: Each Teams Phone user must receive a Teams Phone license and must also be voice-enabled. Source: [Set up Teams Phone in your organization](https://learn.microsoft.com/en-us/microsoftteams/setting-up-your-phone-system), Step 1: Buy and assign a Teams Phone license. Checked 2026-09-06.