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  - The question that always slows provisioning down: "who manages your Azure subscription?" If it's a central IT team that hasn't touched ACS before, add buffer. Number provisioning delays are almost always an Azure approval or admin access issue, not a D365 issue.
  - Clients consistently underestimate DID quantity because they're thinking total headcount, not concurrent calls. Push back on this early with a quick concurrent call estimate before purchase: numbers can't be easily cancelled mid-cycle.
- - ACS PSTN is the right default for most net-new deployments. Only deviate if the client has a carrier relationship they actively want to preserve, or has a country requirement ACS doesn't cover.
+ - ACS PSTN is no longer the default for net-new deployments. With Direct Offer retiring in 2028 and new tenants blocked from buying ACS numbers, design new voice on Teams Phone extensibility, with Calling Plan, Operator Connect or Teams Direct Routing for the numbers. Treat this doc as the reference for estates you're migrating away from.
  
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+ > **Retiring:** standalone Azure Communication Services telephony reaches end of service on 30 September 2028. Teams Phone extensibility is the destination. See [Plan migration from Azure Communication Services](https://learn.microsoft.com/en-us/dynamics365/contact-center/administer/migrate-from-azure-communication-services).
+ 
+ 
  ## What it does
  Azure Communication Services (ACS) is the underlying telephony platform for D365 Contact Center voice. This setup configures an ACS resource, connects it to your D365 instance, and enables inbound and outbound calling via Microsoft-managed PSTN connections. Customers can call your published phone numbers, and agents can dial out using ACS infrastructure.
  
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  - **Caller ID presentation:** Decide if outbound calls show the agent's extension or a main DID
  
  ## Gotchas
+ - **This is now a migration story, not a default.** ACS Direct Offer telephony retires on 30 September 2028, and from 30 September 2026 a tenant without an existing ACS resource can't acquire or port numbers into ACS. Direct Offer moves to Teams Calling Plan via a manual, support-assisted ticket on the Microsoft telephone number services portal — there is no automated path, and ACS numbers in Asia Pacific can't be migrated to Calling Plan at all. For net-new deployments choose Teams Phone from the start. See [ACS retirement and migration](https://365-almanac.app/kb/d365-contact-center/feature-acs-retirement-migration).
+ 
  - ACS provisioning can stall if your Azure account is flagged for fraud review; whitelist IP ranges in advance if possible
  - Changing the ACS resource linked to D365 is disruptive: all in-flight calls drop; plan the cutover carefully
  - Number porting from another carrier *into* ACS is slow (4–8 weeks) and requires carrier sign-off; direct routing is faster for BYOC scenarios
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- *Source last updated: 2026-04-30 | Worth revisiting if ACS pricing shifts or new voice features ship*
+ *Revisit as ACS retirement milestones pass; treat as legacy for net-new design*