The remote nature of the modern workplace poses significant challenges to businesses trying to adapt their communication solutions. Because many workers can now work from anywhere, relying on traditional business telephony systems is no longer sufficient. By using an integrated collaboration platform like Microsoft Teams, organizations can empower their users with unified communication no matter where they are working from.

Microsoft Teams is the hub for teamwork in Microsoft 365 that combines meetings, chat, calling, and collaboration in one platform. Microsoft Teams can also be used as a fully featured business phone system (PBX).

Microsoft Teams Calling supports standard Phone System features, such as call answering and initiating with integrated dial pad, call holding and retrieving, call forwarding and simultaneous ringing, call history, voicemail, and emergency calling.

Organizations can use Microsoft Teams as a PBX in two ways: by using a pre-set Microsoft Teams Calling plan that is integrated within the rest of Teams’ functionality, or by implementing Direct Routing.


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Microsoft Phone System Direct Routing lets you connect a supported Session Border Controller (SBC) to Microsoft Phone System. With this capability, you can configure Public Switched Telephone Network (PSTN) connectivity with the Microsoft Teams client, as shown in the following diagram:

Direct Routing with Microsoft Teams example diagram

A Session Border Controller (SBC) is a special-purpose device that protects and regulates IP communications flows. Additionally, SBCs provide a level of security by protecting against Denial of Service (DoS) and Distributed DoS (DDoS) attacks, safeguarding against toll fraud and service theft, and providing signaling encryption.  The SBC may be hosted on-premises, in the cloud, or by a third party.

Session Initiation Protocol (SIP) Trunks are connections between a business phone system, the internet, and the PSTN. SIP Trunks are essential for connecting your PBX to the PSTN.

Direct Routing is a great solution for organizations who want to leverage the reliability and collaboration features of Microsoft Teams, but have particular circumstances that require connection to a third-party telephony provider:

  • The Microsoft Calling Plan is not available in one of the organization’s locations. This is a common roadblock for global organizations.
  • The organization requires connection to third-party analog devices, call centers, and so on.
  • The organization has an existing contract with a PSTN carrier.

Additionally, a business that has limited IT support bandwidth may benefit from the support provided by external telephony providers. A managed business phone solution removes complexity from the integration and can provide a seamless migration to Teams Calling.

There are many great options for customers wanting a fully managed, device-as-a-service, hosted SBC/Direct Routing solution complete with monitoring, management tools, and reporting. These solutions enable integration with other devices and applications to further enhance the service including call recording, analog devices, call center, etc.

Utilizing Direct Routing with Teams Calling has several great benefits:

  • Unified communication and collaboration platform: By combining your organization’s internal communications and external communications, you empower your users with a platform that combines chat, meetings, calling, and file sharing all in one location.
  • Calling and Teams features: By using Teams as your PBX via Direct Routing, you can utilize all the features inherent in Microsoft Teams (file collaboration, Office 365 app integration, video meetings, etc.) while also taking advantage of a breadth of PBX features including call transfer, queues, auto-attendant, location-based call routing, simultaneous ring, Microsoft Teams Rooms, and more.
  • Communicate from anywhere: Direct Routing with Microsoft Teams makes it possible to work from anywhere while still communication and collaborating seamlessly. Teams as your business phone allows your users to make and receive calls from their landline phones, Teams client, and mobile devices.
  • Time and costs savings: Using Teams Calling with Direct Routing can save your business significant costs with licensing, call rates, and IT support.
  • Keep your old numbers: With Direct Routing, you can keep your existing numbers and assign any new numbers you need. This will save you time and resources so you can maintain continuity and identity with your current phone numbers.
  • Flexibility with preferred providers: Direct Routing with Teams Calling allows you to pick your preferred provider to manage and host your business phone system, providing you more control and flexibility over your communications.


While businesses that opt to use Direct Routing with an external telephony provider will not need to purchase a Microsoft Teams Calling plan, they will still need the following licenses:

  • A Microsoft Phone System License for every user who will need to be able to dial a PSTN number on the business phone. This can be fulfilled through the Office 365 E3 or E5 license.
  • A Microsoft Audio Conferencing license is required to add external participants to scheduled meetings. This can be found as part of the E5 license or as an add-on for the E3 license.

Organizations who use Direct Routing will also have the costs for the calling plans from their telephony service provider, as well as the costs for the Direct Routing solution, which varies based on the provider and model they choose, such as on-premises SBC, fully hosted, or managed.


As organizations adapt to a modern, remote workforce, it is essential that they prioritize enabling their users to work efficiently from anywhere. Adopting the Microsoft Teams platform as a business phone system makes calling simple while being able to seamlessly move between chat, calls, meetings, and collaboration features.

By using Direct Routing with Teams, organizations can use their own telephony carrier for PSTN connectivity while leveraging the unified communication and collaboration features of Microsoft Teams.

Apex’s Ignite for Microsoft Teams service offering will empower your organization to streamline collaboration and unleash the power of teamwork across your entire organization. Apex Digital Solutions can assist with the evaluation, purchase, deployment, and success management of Microsoft Teams. Learn More >>