There are three ways to connect Microsoft Teams Phone to the public telephone network. Microsoft will tell you all three work. That's true. What Microsoft won't tell you is that they carry meaningfully different long-term implications for how much control you retain over your own voice infrastructure.

Here's what each option actually is, and why the choice matters more than most IT buyers realize.

Microsoft Calling Plans

Microsoft Calling Plans means Microsoft is your carrier. You buy voice minutes from Microsoft through the Teams admin center, and Microsoft handles the connectivity to the PSTN.

This is the simplest option to set up. There's no third-party carrier involved, no SIP trunk to configure, no Direct Routing infrastructure to manage. For small organizations that don't want to deal with any of that complexity, it's a reasonable starting point.

The tradeoffs are straightforward. Microsoft's per-minute rates are not competitive for high-volume calling environments. Geographic coverage has gaps — not every country or region is supported. And you're completely dependent on Microsoft for voice service continuity.

For an organization running meaningful outbound volume, or operating internationally, Calling Plans typically fail on cost and coverage before they become a strategic concern.

Operator Connect

Operator Connect is a Microsoft-certified carrier program. Approved carriers — including large telcos and specialized providers — connect to Teams through a standardized API that Microsoft manages. You select a carrier from the Operator Connect marketplace in the Teams admin center, provision numbers, and the carrier handles the PSTN connection.

The setup experience is cleaner than Direct Routing. There's no SIP proxy to manage, no Session Border Controller to configure. The carrier relationship is managed through the Teams interface.

Here is what Operator Connect does not tell you in the product sheet: the network points only to Microsoft Teams. There is no path to redirect traffic to a different application. If your organization decides to add a contact center that sits outside Teams, move some users to a different platform, or simply evaluate other voice applications, you cannot redirect that traffic. You would have to port numbers out.

This isn't a carrier flexibility problem. Switching carriers within the Operator Connect ecosystem is straightforward — you can move between OC providers without rebuilding anything. The constraint is at the application layer. The network knows only one destination: Teams.

In an environment where voice applications are changing — AI agents, contact center platforms, unified communications — that constraint is worth understanding before you sign.

Direct Routing

Direct Routing connects Teams to a carrier through a Session Border Controller that you or your provider manages. The SBC sits between the Teams environment and the carrier network, handling the SIP signaling translation.

This is more complex to deploy than Operator Connect. It requires SBC configuration, carrier provisioning, and ongoing management. Done poorly, it creates problems. Done well, it gives you something Operator Connect and Calling Plans cannot: application-agnostic network routing.

With Direct Routing, the carrier relationship and the application layer are separate. The network is not locked to Teams. If you add a Five9 contact center, route a subset of users to a different platform, or pilot a new AI voice application, you can direct traffic there without porting numbers and without rebuilding your voice environment. The application changes. The network doesn't have to.

This matters because the pace of application change in enterprise voice is accelerating. Two years ago, most organizations weren't evaluating AI voice agents. Today many are. What they have next year is unclear. The organizations that built their voice infrastructure on a platform-agnostic foundation will have significantly more flexibility — and lower switching costs — as those decisions play out.

The Question That Defines the Right Choice

Most buyers evaluate these options on cost, complexity, and features. Those are reasonable criteria. But the question that actually differentiates them is simpler:

Do you need your voice network to be tied to one application, or do you need it to be able to point anywhere?

If your voice environment is Teams and you're confident it will stay that way, Operator Connect is a clean, well-supported option. If you're running Teams as one of several voice applications, or if you anticipate that your application architecture will change, Direct Routing gives you the architectural flexibility that Operator Connect cannot.

We have deployed over 400 Teams Phone environments since 2019. The organizations that have the most flexibility today are the ones that separated their carrier layer from their application layer when they built. The ones that didn't have learned that lesson when the next application change came around.

The Bottom Line

Microsoft Calling Plans is simple but expensive at scale. Operator Connect is clean to set up but locks your network to Teams. Direct Routing is more complex to deploy but gives you application-agnostic routing that compounds in value as your voice stack evolves.

How you deploy matters more than what you deploy. The architecture you choose today determines how much the next change costs you.