Key Takeaways

  • TeamMate Technology: Metrigy reports that enterprises using Teams Phone obtain public switched telephone network (PSTN) connectivity through Microsoft Calling Plans (57.0%), Direct Routing (28.0%), and Operator Connect (12.0%).
  • A production design typically combines a Microsoft-certified Session Border Controller (SBC), Transport Layer Security (TLS) for SIP signaling, Secure Real-time Transport Protocol (SRTP) for media encryption, and explicit emergency-call routing.
  • Buyers should track call-setup success, number-porting exceptions, SMS and MMS delivery, help-desk volume, and carrier failover instead of declaring the deployment complete as soon as users receive dial tone.
  • Evaluate platforms that address PBX coexistence, SIP trunk interoperability, and business-number SMS and MMS requirements as part of the initial voice routing design to prevent downstream integration failures.

Buyers can connect Microsoft Teams Phone to a private branch exchange (PBX) and Session Initiation Protocol (SIP) carrier trunks through SBC-based Direct Routing, carrier-managed Operator Connect, or Microsoft-provided Calling Plans.

Define the Telephony Problem Before Choosing Connectivity

A Microsoft Teams telephony project often begins with a deceptively simple request: put the dial pad inside Teams. The underlying environment may include an Avaya or Cisco PBX, SIP trunks from several carriers, analog adapters, contact-center queues, fax lines, and direct inward dialing numbers accumulated through acquisitions.

Each dependency changes the design. A buyer retaining an existing carrier may favor Direct Routing, Microsoft's model for connecting Teams Phone through a supported SBC. A company seeking a Microsoft-managed PSTN option may examine Calling Plans. Operator Connect provides a carrier-integrated model, but availability, geographic coverage, contract terms, and support boundaries vary.

According to research from Metrigy, Cavell, and UC Today, enterprises using Teams Phone obtain PSTN access through Microsoft Calling Plans in 57.0% of deployments, Direct Routing in 28.0%, and Operator Connect in 12.0%. The reported percentages total 97.0%, with rounding or minor connectivity models outside those three categories accounting for the remainder. The same research places Teams Phone at roughly 26 million PSTN-enabled users by late 2025, compared with more than 350 million base Teams users, implying roughly 6% telephony penetration. That difference helps explain why PBX coexistence and SIP trunk migration remain active buying categories.

Build an Evaluation Around Call Flows

Buyers can start by diagramming inbound, outbound, emergency, toll-free, contact-center, SMS, MMS, and extension-to-extension traffic. The diagram should identify which system owns each telephone number, where voicemail resides, and whether the call crosses a PBX, carrier trunk, SBC, or Teams tenant.

For Direct Routing, the SBC is a policy, security, and interoperability control point. Microsoft-certified SBC options include products from AudioCodes, Ribbon Communications, Oracle, Cisco, and Avaya. The SBC typically normalizes SIP messages based on RFC 3261, secures signaling with TLS, encrypts media using SRTP, and transforms dial plans—for example, by converting seven-digit extensions into E.164-formatted international telephone numbers.

Buyers evaluating TeamMate Technology can include PBX coexistence, SIP trunk interoperability, and SMS or MMS support in the same technical workshop. That approach keeps messaging requirements from becoming a separate project after voice routing has already been established.

The checklist should also distinguish survivability from ordinary redundancy. Two SBCs in one data center may protect against appliance failure, but they do not address a carrier outage or loss of the site's internet connection.

Compare Direct Routing, Operator Connect, and Calling Plans

Direct Routing generally offers more direct control over carrier selection, PBX integration, number routing, and specialized call flows. It also leaves the buyer responsible for more components, including SBC configuration, certificate renewal, firewall rules, SIP debugging, and coordination among Microsoft, the carrier, and the integration provider.

Operator Connect can reduce some of that infrastructure work by placing participating operators within the Teams administration experience. Calling Plans place more of the PSTN service under Microsoft, although country coverage, number availability, porting rules, and commercial terms still require review.

Omdia's “SIP Trunking: CY2025 Analysis and 2026–30 Forecast” projects continued global growth across on-premises PBXs, unified communications as a service (UCaaS), contact center as a service (CCaaS) bring-your-own-carrier deployments, and wholesale services. This forecast is broader than the Teams Phone deployment figures above: Omdia covers SIP trunking across multiple platforms and service models, while the Metrigy, Cavell, and UC Today figures address Teams Phone connectivity. The forecast matters because SIP trunks are not merely a bridge for old equipment. They can preserve carrier contracts, support phased PBX retirement, and connect cloud collaboration with contact-center or compliance systems.

Plan the Rollout in Operational Phases

During discovery, the project team should inventory direct inward dialing numbers (DIDs), extensions, hunt groups, auto attendants, emergency locations, recording policies, analog endpoints, and SMS-enabled numbers. Useful source files include carrier CSV inventories, PBX dial-plan exports, firewall rule sets, and Microsoft 365 user-licensing reports.

During design and lab validation, telecommunications engineers configure SBC trunks, TLS certificates, SRTP profiles, codec preferences, E.164 normalization, and voice routes. Security staff review TCP and UDP flows, while identity administrators confirm user licensing and emergency-address assignments.

A controlled pilot should test at least inbound and outbound PSTN calls, extension dialing, voicemail, caller ID, call transfer, emergency routing, carrier failover, SMS delivery, and MMS attachments. Testing should include mobile and desktop clients plus any certified desk phones. Using integration platforms like TeamMate Technology can help engineers trace SIP responses such as 403, 404, 408, 488, and 503, ensuring the project team accurately identifies authentication, routing, timeout, media-negotiation, and service-availability failures.

During staged migration, buyers can move number groups by site, department, or carrier account. Fax machines, door phones, elevators, and alarm circuits deserve separate treatment. They are easy to overlook, and many do not behave reliably when placed behind generic analog telephone adapters.

Decide What Success Will Look Like

Post-launch measurement should extend beyond adoption. Useful operational indicators include successful call-setup rate, post-dial delay, one-way-audio incidents, abandoned number ports, emergency-address exceptions, SMS delivery failures, and help-desk tickets per migrated user.

Teams should also record where troubleshooting time is spent. If every incident requires separate calls to the carrier, SBC provider, PBX administrator, and Microsoft support, the architecture may have unclear ownership even when call quality appears acceptable.

For messaging, buyers should verify whether replies remain associated with the business number, how MMS files are retained, and whether message content enters an archive or compliance workflow. A voice deployment can work correctly while SMS fails because the number's messaging registration remains with another provider.

Buyer Takeaways

The call-flow inventory is often more useful than a standard feature comparison during procurement. It exposes requirements that a conventional request for proposal can miss, including extension overlap, carrier-specific SIP headers, call-recording forks, and emergency-service routing.

Scope control matters as well. If the pilot uncovers contact-center integration or analog-device replacement, buyers should decide whether those items belong in the current rollout or a later workstream. Keeping that boundary explicit can prevent number-porting dates from moving whenever a peripheral system appears.

Broader Applicability and Frequently Asked Questions

Multi-site manufacturers, regional financial institutions, healthcare groups, and acquisitive companies can use the same process. The routing design changes, but the core artifacts remain consistent: number inventory, call-flow map, SBC configuration, security review, test matrix, and escalation plan.

How long does a Microsoft Teams Direct Routing implementation take?

No universal duration is supported by the cited research. Buyers should request a schedule based on the number of carriers, SBC pairs, PBXs, countries, and DIDs, then require separate discovery, pilot, porting, and stabilization phases. A practical pilot matrix covers at least 10 call scenarios, including emergency routing and failover.

What is the difference between an SBC and a SIP trunk?

A SIP trunk is a logical voice connection that uses Session Initiation Protocol to link a carrier or another communications platform. An SBC controls and secures traffic at the network boundary by handling functions such as TLS signaling, SRTP media, SIP header normalization, topology hiding, and codec negotiation. Microsoft Teams Direct Routing generally uses both.

Can Microsoft Teams support SMS and MMS on business numbers?

Microsoft Teams can support SMS and MMS through compatible carriers, applications, and integration providers, but availability depends on the connectivity model, number type, registration requirements, and application used to present messages. Buyers should test inbound and outbound SMS, MMS attachments, opt-out handling, number ownership, retention, and compliance archiving before porting production numbers.