Short answer
Each user who needs a phone number requires a Microsoft Teams Phone Standard or E5 licence, and your Microsoft 365 tenant must be in Teams-Only mode. If you are not licensed yet, FirstNet can supply Teams Phone licences as a Microsoft CSP.
In detail
What to check before you start:
- Teams Phone Standard, or E5 which includes Teams Phone, for every user who will make or receive external calls.
- Teams-Only mode in the tenant.
- Audio Conferencing licences where users need them for meetings.
- A Global Admin available for the integration window.
- A FirstNet voice plan: Voice Bundles with inclusive minutes, or Voice Rate Options with per-minute rates.
You do not need Microsoft Calling Plans to use FirstNet. Operator Connect or Direct Routing provides the phone numbers and calling instead, and both can still coexist with Calling Plans in the same tenant if some users stay on them.
In the Prepare phase, FirstNet reviews your licensing inventory, tenant readiness, federation and existing voice routing, then gives you a readiness checklist of anything to fix before go-live. Where licences are needed, FirstNet can supply them alongside the calling service, so licences and voice sit on one contract.
Source: FirstNet Microsoft Teams Calling service page →
Didn’t answer your question?