Microsoft Direct Routing is the method of connecting Microsoft Teams Phone to the public telephone network through your own carrier and a Session Border Controller, rather than through Microsoft's native carrier options. It gives organizations the ability to bring their own voice infrastructure to Teams — their own carrier relationships, their own numbers, their own routing architecture — while using Teams as the calling application for their users.
It is the more complex of the three ways to connect Teams to the PSTN. It is also the one that gives organizations the most long-term control over their voice environment.
How It Works
Every phone call that goes in or out of Microsoft Teams has to traverse the public telephone network at some point. Microsoft Teams itself is a cloud application — it handles the user interface, the call management, the collaboration features. What it does not natively include is a connection to the PSTN.
Direct Routing makes that connection through two components. The first is a Session Border Controller — an SBC — which sits at the boundary between the Teams environment and the carrier network. The SBC translates between the SIP signaling that carriers use and the protocols Teams requires. It handles call setup, teardown, codec negotiation, and the security requirements Microsoft specifies for Direct Routing certification.
The second component is the carrier. With Direct Routing, the organization selects its own carrier, provisions its own SIP trunks, and connects those trunks to the SBC. The carrier handles the actual call delivery to and from the PSTN. The SBC handles the translation between the carrier and Teams.
Microsoft certifies specific SBC models and vendors for use with Direct Routing. The configuration requires proper Teams dial plan setup, voice routing policies, and PSTN usage records in the Teams admin center. Done correctly, it is invisible to end users — calls work exactly as they would with any other Teams calling option.
Direct Routing vs. The Alternatives
Microsoft offers three ways to connect Teams Phone to the PSTN: Calling Plans, Operator Connect, and Direct Routing. Understanding why organizations choose Direct Routing over the others comes down to one question: how much control do you need over the carrier layer?
Calling Plans put Microsoft in the role of carrier. Operator Connect brings in a certified third-party carrier through a Microsoft-managed marketplace. Both are simpler to deploy than Direct Routing. Both also mean the carrier relationship is managed through Microsoft's framework, with Microsoft's pricing structures and Microsoft's constraints on how numbers are provisioned and routed.
With Direct Routing, the carrier relationship is entirely separate from Microsoft. Organizations negotiate their own rates, choose from a broader set of carrier options, and retain full control over how their numbers are provisioned and how their calls are routed. For organizations with existing carrier agreements, high call volumes where per-minute costs matter, or international footprints that Microsoft's Calling Plans do not cover, Direct Routing is typically the more practical path.
The more significant difference is architectural. With Operator Connect, the carrier network points to Teams and only Teams. If the organization ever wants to route traffic to a different application — a contact center, an AI voice agent, a different UCaaS platform — numbers have to be ported out. The architecture does not support pointing traffic elsewhere.
With Direct Routing, the SBC layer creates application-agnostic routing. The same carrier infrastructure can route calls to Teams, to a Five9 contact center, to an AI voice agent, or to any other SIP-capable application. Numbers live in the carrier network, not inside Teams. As the organization's voice application stack evolves, the carrier layer accommodates the changes without requiring a rebuild.
What Direct Routing Requires
Direct Routing is not a DIY project for most organizations. The SBC configuration requires knowledge of SIP, Microsoft's specific Direct Routing requirements, and the carrier's provisioning specifications. Teams dial plans and voice routing policies require accurate setup or call routing fails in ways that are not always immediately obvious to end users.
The ongoing management requirements are real too. SBC firmware updates, carrier changes, Teams policy updates, and number porting events all require someone who understands the carrier and application layers simultaneously. Organizations that treat Direct Routing as a one-time deployment and not an ongoing managed service tend to accumulate configuration debt that surfaces as call quality problems and routing failures over time.
We have deployed Direct Routing across 400+ Teams Phone environments since 2019. The failure modes we see most consistently are not hardware or carrier failures — they are configuration mismatches between the SBC, the carrier provisioning, and the Teams dial plan that nobody caught at deployment and nobody maintained afterward.
The organizations with the healthiest Direct Routing environments are the ones that treat it as a managed voice infrastructure, not a completed IT project.
The Bottom Line
Direct Routing is how organizations bring their own carrier to Microsoft Teams. It is more complex to deploy than Calling Plans or Operator Connect, and that complexity is worth it for organizations that need carrier choice, cost control, or an application-agnostic voice architecture that can accommodate whatever comes next.
The architecture is right for most enterprise deployments. The execution is what determines whether it performs.
