Connecting Microsoft Teams to the PSTN: What Service Providers and Contact Centers Need to Know
There was a time when video conferencing felt like a nice-to-have. Businesses had their PBXs, desk phones, and the occasional conference call. Then 2020 happened.
Almost overnight, platforms like Microsoft Teams, Zoom, and Webex went from useful tools to essential infrastructure. The technology had existed for years — it just took a stay-at-home mandate for it to reach widespread adoption.
Now that the dust has settled, these video-first platforms have become serious players in the voice market. And for MSPs and UCaaS vendors who’ve built their offerings around them, there’s a growing demand to answer: how do you get Teams talking to the rest of the phone network?
Why PSTN Connectivity Matters
Microsoft draws a clear line between Teams Phone — peer-to-peer calling within the platform — and Teams Phone with PSTN, which is a separate license that extends calling to the public telephone network.
For contact centers, support centers, and any business that runs on inbound and outbound calling, that second license is non-negotiable. It’s also where the interconnection work begins — and where MSPs, ISPs, and system integrators come in to make it actually work.
The Interoperability Challenge
Connecting Teams to the PSTN is more nuanced than dropping in a SIP trunk.
Teams uses SIP, but with its own requirements: TLS and SRTP for encryption, specific handling of RTCP analytics multiplexed within RTP streams — something standard SIP trunks don’t do — and particular expectations around signaling. If any of these elements don’t align between Teams and your carrier, calls fail or drop unexpectedly.
On the carrier side, you’re dealing with different SIP interfaces, various codecs, and networks with their own adaptations. For system integrators who’ve spent time bridging enterprise PBXs to carrier trunks, this will feel familiar — but Teams adds a layer of specificity that a generic SIP proxy won’t handle cleanly.
Where Session Border Controllers Fit In
An SBC sits between Teams and the rest of the network, handling the translation and security that makes interoperability work. It decrypts packets where needed, normalizes SIP messaging across carriers, and provides the routing logic to get calls where they’re going.
Beyond basic connectivity, SBCs deliver the redundancy service providers need to build reliable offerings. If one carrier route goes down, traffic shifts automatically. Fraud protection, access control, and call detail records for billing and troubleshooting are all part of the picture.
For Teams specifically, Microsoft’s Direct Routing program defines what an SBC must support: certificate exchange, FQDN-based configuration, and the RTCP-in-RTP handling mentioned above. It’s close enough to standard SIP that the concepts are familiar, but specific enough that you need a platform built to meet the spec.
What It Takes to Set Up Teams Direct Routing
On the Microsoft side, administrators configure licenses and enable outbound calling permissions — by default, Teams is internal only. For MSPs managing this across multiple customer accounts, knowing the Teams admin center well matters.
On the SBC side, it’s certificates, domain settings, and routing logic. You’re establishing a trusted path between the Teams environment and your voice network, with the SBC handling security and adaptation at the boundary.
Once it’s configured, it runs like any other SIP trunk operationally. The complexity is in the initial setup, not day-to-day management — which is relevant for MSPs running this at scale.
A Growing Opportunity for Service Providers
More businesses are consolidating voice, video, and messaging into unified platforms, and they still need to connect to the broader telephone network when they do.
For MSPs, this is an opportunity to deepen value in existing accounts. For ISPs and system integrators, it opens a path into a growing segment of enterprise customers who’ve standardized on Teams but need a reliable voice interconnection partner. The providers who can deliver that without interoperability headaches will be well-positioned as this market continues to grow.
ProSBC Now Supports Teams Direct Routing
ProSBC now supports Microsoft Teams Direct Routing. Existing customers can add Teams connectivity to their deployments without replacing current infrastructure — meaning service providers can extend their voice offerings to Teams customers without starting from scratch.
The add-on includes TLS and SRTP support, certificate management, and the specific SIP handling that Direct Routing requires. It’s designed to work alongside existing carrier connections, so you can bring Teams into your stack without disrupting what’s already working.
Curious how Teams Direct Routing fits into your network? Contact us to explore your options.
Want the Full Conversation?
For a deeper dive into connecting Microsoft Teams to the PSTN — including the technical details and real-world considerations — check out our latest podcast episode. We unpack these challenges and discuss what service providers should be thinking about as unified communications continues to evolve.
