Understand who operates the calling service
Microsoft Calling Plans use Microsoft as the telephone operator. Operator Connect connects Teams to a participating certified operator. Direct Routing connects a chosen carrier through a certified session border controller, with operation assigned to your team or a provider.
Teams Phone Mobile is a separate option for supported mobile operators. More than one connectivity model can be used within a tenant. Source: Microsoft’s PSTN connectivity documentation.
Compare the operating responsibilities
| Approach | Operating model | Ask before shortlisting |
|---|---|---|
| Calling Plans | Microsoft provides telephone service. | Does the offered plan cover the locations, number types, calling patterns, and support you need? |
| Operator Connect | A certified operator supplies the telephone service and integrates with Teams. | Which countries, porting tasks, service commitments, and support boundaries are included? |
| Direct Routing | A certified SBC connects the carrier. Its management must be assigned. | Who runs the SBC, tests resilience, handles incidents, and maintains any required integration? |
Model descriptions: Microsoft. Evaluation questions are our guidance. Avoid selecting a model solely from the employee count.
Check the licences you actually hold
Microsoft documents Teams and Phone System entitlements separately from PSTN connectivity. Microsoft 365 E5 includes Phone System; an E5 “no Teams” subscription still needs the appropriate Teams entitlement. Microsoft lists combinations such as Teams Enterprise plus E5 (no Teams), and Teams Enterprise plus Teams Phone Standard.
Confirm the exact subscription names, assigned users, and calling service before purchasing additional licences. Resource accounts and shared devices need their own review. Source: Microsoft Teams Phone licensing.
For a nonprofit organization, ask the licensing provider to confirm eligibility, the specific nonprofit subscriptions held, and the current calling offer in writing. Do not build the case from a commercial price list or an assumed discount. Request a dated quote showing recurring charges, usage, migration work, and any contract commitments.
Use the same framework at 1,000 or 7,500 employees
These are planning scenarios, not size thresholds for a particular model. At either scale, identify who needs external calling, who only needs collaboration, which sites have special requirements, and who will administer the service.
For a larger rollout, ask whether the operating team can manage changes across locations and whether a staged deployment is practical. For a smaller rollout, verify the same support and continuity requirements. Complexity comes from the environment and the required service, as well as the number of users.
Prepare a pilot before a migration commitment
Give each shortlisted provider a representative calling scenario. Include a user, a location, the current number, the call flow, and the systems that must work together. Ask the responsible specialists to include emergency calling requirements and location configuration in the test plan.
Agree who approves number porting, how failed tests are handled, how users receive support, and when the current service can be disconnected. Use the Decision Brief to record the business need first; the detailed number inventory can follow during discovery.
Put the research to work
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