Shared calling: PSTN for the many
One resource account with one number + calling plan/route; a shared calling policy attaches a population to it. Everyone in the policy makes outbound calls presenting the shared number and receives via the attached AA — no per-user DIDs, no per-user calling plans. The economics: frontline and desk-light populations get real PSTN at a fraction of per-DID cost.
The trade-offs to state up front: no personal number (callbacks hit the AA), and emergency calling needs care — emergency calls from shared-calling users use dynamic location/emergency numbers configuration; validate per country before rollout, not after.
SBA: the branch that won't die
Direct Routing branches have a single dependency: the path to Microsoft. A Survivable Branch Appliance (SBA — vendor software on the branch SBC) breaks the dependency for voice:
- Normal times: clients register their possible survivability relationship; calls flow normally via Microsoft.
- WAN/Microsoft unreachable: Teams clients in the branch detect it and register to the LOCAL SBA; PSTN calls in/out continue through the branch SBC's local trunk. Internal branch calls keep working.
- Degraded honestly: no meetings, no chat, no presence, no voicemail — it is a survival mode for dial tone, not a mini-cloud.
- Recovery: connectivity returns, clients re-register to the service, the SBA goes quiet. Ideally nobody noticed.
What to watch (proofs)
- Shared calling wiring:
Get-CsTeamsSharedCallingRoutingPolicy | fl(in the nightly scan) — the resource account and emergency numbers list per policy; the assignment census tells you who lives on shared calling. - Emergency validation: test calls per the country's test procedure (e.g. 933-type services where offered) from a shared-calling user BEFORE go-live; keep the evidence.
- SBA readiness:
Get-CsTeamsSurvivableBranchAppliance/...AppliancePolicy(both in your scan — they exist in the tenant surface list) — appliance registration and user policy mapping; an SBA nobody assigned users to protects no one. - The only real proof: a scheduled failover TEST — drop the branch WAN in a window, confirm dial tone, log call success, restore. An untested SBA is a hope, not a control.