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Telephony concepts

Warning

Azure Communication Services is introducing breaking changes, and some services are being retired. Learn more in the retirement and breaking changes guide.

Important

SMS and PSTN capabilities depend on the phone number you use and the country/region that you're operating within as determined by your Azure billing address. For more information, visit the Subscription eligibility documentation.

Azure Communication Services Calling SDKs enable you to add telephony and Public Switched Telephone Network (PSTN) access to your applications. This page summarizes key telephony concepts and capabilities. See the calling library to learn more about specific SDK languages and capabilities.

Telephony overview

Whenever your users interact with a traditional telephone number, the Public Switched Telephone Network (PSTN) voice calling handles the call. To make and receive PSTN calls, you need to add telephony capabilities to your Azure Communication Services resource. In this case, signaling and media use a combination of IP-based and PSTN-based technologies to connect your users. Going forward, Communication Services supports only Teams Phone connectivity. For more information about the retirement of the legacy telephony options (Azure Communication Services Direct Offer and Direct Routing), see Azure Communication Services telephony retirement.

Teams Phone connectivity

As organizations increasingly adopt Microsoft Teams for their collaboration and communication needs, understanding the various PSTN connectivity options available becomes crucial. With Teams Phone, you have three primary options:

  1. Calling Plans are an all-in-the-cloud solution in which Microsoft acts as your PSTN carrier. Calling Plans are the simplest option, ideal for organizations that don't need to retain their current PSTN carrier. By using Calling Plans, you get Teams Phone with added Domestic or International Calling Plans for your solution to reach phone numbers around the world.

    This option doesn't require any on-premises deployment or maintenance. For more information, see Microsoft Teams Calling Plans.

    Diagram shows the simplest solution Teams Phone system with Calling Plan using Microsoft as a public switched telephone network (PSTN) carrier.

  2. Operator Connect enables you to bring your existing PSTN carrier into the Microsoft Teams environment. If your carrier participates in the Microsoft Operator Connect program, they can manage PSTN calling and Session Border Controllers (SBCs) for you.

    Operator Connect provides a fully managed service with no hardware footprint. This option is a great choice for organizations that want to maintain their existing PSTN infrastructure while using Teams. For more information, see Plan for Operator Connect.

    Diagram shows Teams Operator Connect using a public switched telephone network (PSTN) and Session Border Controller as a Service (SBCaaS) through Teams Phone / Teams Admin Center to connect your operators.

  3. Direct Routing enables you to use your own PSTN carrier by connecting your SBCs to Teams Phone. Direct Routing offers the most flexibility, enabling you to design a solution that fits complex environments or manage a multi-step migration.

    Direct Routing is suitable for organizations that need to retain their current PSTN carrier and have specific requirements for interoperability with third-party private branch exchanges (PBXs), analog devices, and other telephony equipment. For more information, see Plan Direct Routing.

    Diagram shows Teams Direct Routing. It features Teams users on Microsoft 365 through on premises session border controller (SBC), phone number ranges, and third party private branch exchange (PBX) / telephony equipment connecting to a telephony trunk and public switched telephone network (PSTN).

If you answer yes to the following questions, then Teams Phone connectivity options are the right solution for you:

  • Teams Phone services are available in your region.
  • You want Microsoft‑managed PSTN access through Calling Plans, prefer simplified onboarding with Operator Connect, or want to bring your own carrier and connect your SBC.
  • You plan to integrate contact center or advanced workflows by using Teams Phone Extensibility (TPE).

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