Short answer
Yes. FirstNet Teams Direct Routing is carrier-agnostic, so FirstNet's managed SBCs can sit on top of your existing SIP environment while your carrier relationship stays in place. Users get Teams calling now, without waiting for the carrier contract to end.
In detail
How it works:
- FirstNet connects your Teams tenant to Microsoft-certified SBCs that it owns and manages, so there is no SBC to buy.
- The SBCs route calls out through your existing carrier's SIP trunk, or through FirstNet's own trunk if you choose.
- Signalling is encrypted with TLS 1.2 and media with SRTP.
- Custom routing, such as location-based rules and custom dial plans, is designed against your tenant.
When the carrier contract comes up for renewal, you can move the trunk to FirstNet SIP termination and port your numbers with a signed Letter of Authority, without changing how users call in Teams.
Keep in mind how support is split. FirstNet's SLA covers what it manages: the SBC platform, its own SIP trunk, number provisioning and support. A third-party carrier you keep sits outside that SLA. FirstNet still acts as the single point of escalation for the Teams calling service, including joint escalation with Microsoft.
Source: FirstNet Microsoft Teams Calling service page →
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