Microsoft Teams Phone architecture and licensing

Verified 2026-09-06 · 35 claims · sources tier 2

Also known as Cloud PBX, Microsoft Phone System, Phone System, Teams Phone.

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.
• See also Teams Operator Connect and Azure Communication routing.
• See also Teams emergency calling and location policies.
• See also Teams call quality dashboard and analytics.
• See also Teams contact center integration models.
• See also Identity SSO and directory provisioning for UC.
• See also Webex Calling architecture and deployment models.
• See also Teams voice routing policies and dial plans.

Applicability

Across the claims in this article, the evidence covers Microsoft Teams Phone across cloud, customer-managed-sbc, direct-routing-sba, and operator-managed-pstn deployments, verified as of 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 any claim in this article:

• Defining supported Teams Phone and Webex Contact Center coexistence patterns is not covered by any claim in this article.
• Mapping emergency routing and location duties by country and PSTN model is not covered by any claim in this article.
• Building a provider-specific number port and rollback runbook is not covered by any claim in this article.
• Mapping CUCM and Webex Calling objects to Teams Phone objects is not covered by any claim in this article.
• Determining which Cisco endpoints can be reused with Teams Phone is not covered by any claim in this article.
• Building a dated operator and number coverage inventory by country is not covered by any claim in this article.
• Resolving the supportable CAE design for branches that require SBA is not covered by any claim in this article.

WarmTransfer. (2026, September 6). Microsoft Teams Phone architecture and licensing. WarmTransfer. https://warmtransfer.net/knowledge/teams-phone-architecture

@misc{warmtransfer-teams-phone-architecture,
  title  = {Microsoft Teams Phone architecture and licensing},
  author = {{WarmTransfer}},
  year   = {2026},
  url    = {https://warmtransfer.net/knowledge/teams-phone-architecture},
  note   = {Verified 2026-09-06}
}