If your organization runs Teams for collaboration and you are now looking at moving voice across, the first question that matters is: how do you connect Teams Phone to the public telephone network? This is not the same as picking Microsoft Teams. It is a separate architecture decision, and the wrong call at this stage creates problems that take years to unwind.
Microsoft offers four PSTN connectivity models. They are not interchangeable. And for most enterprises with users spread across multiple countries, a mix of existing infrastructure, and a migration timeline that cannot afford a stall, one model alone will not cover every scenario.
Teams Phone is Microsoft's cloud PBX. It adds enterprise calling features — auto attendants, call queues, voicemail, call recording — to the Teams platform. Internal calls between Teams users stay on VoIP and never touch the public network. The moment a user needs to call an outside number, you need PSTN connectivity.
That connectivity is not bundled with Teams Phone licensing. The license covers the PBX capability. PSTN access is arranged separately, through one of four models. As of late 2025, roughly 26 million Teams users have PSTN calling enabled — around 6% of the total Teams user base. The majority of organizations that run Teams have not yet migrated their voice workloads. For most enterprise IT teams, this decision is still ahead of them.
Microsoft becomes your PSTN carrier. Phone numbers are purchased and managed through Microsoft, SLAs run at 99.999%, and there is no separate carrier contract or SBC infrastructure to deal with.
Calling Plans are available in approximately 34 countries. For organizations contained within that footprint — primarily the US and Western Europe — with limited existing carrier commitments, this is the fastest path to deployment. It is straightforward to administer and integrated with the Microsoft stack.
Outside those markets, Calling Plans are not an option. Organizations with existing infrastructure, carrier contracts they need to preserve, or users in countries beyond Microsoft's coverage will hit the ceiling quickly.
A Microsoft-certified third-party carrier manages PSTN access and the underlying SBC infrastructure. You pick a provider from the certified list — 109 operators across 106 countries as of mid-2025 — connect them to your tenant through the Teams Admin Center, and assign numbers to users directly. No hardware on your side.
This model suits enterprises that want carrier-managed PSTN with broader geographic reach than Calling Plans, without the complexity of managing their own SBC estate. Deployment is fast. The management interface is centralized in Teams Admin Center. Pricing from certified operators is often more competitive than Calling Plans at scale.
The constraint is the operator's own footprint. If your chosen carrier does not cover a particular country or cannot meet a specific compliance requirement in a given jurisdiction, you need a secondary solution for those gaps.
Direct Routing connects Teams Phone to any PSTN carrier — certified or otherwise — through a Session Border Controller. The SBC can sit on-premises, in the cloud, or be delivered as a managed service (Direct Routing as a Service).
You can keep an existing carrier relationship and infrastructure in place. You can integrate analog devices, legacy PBX systems, or specialist call routing. You can cover countries where no Operator Connect provider has presence. And you can meet regulatory requirements — survivability, data residency, specific routing obligations — that cloud-only models cannot accommodate.
Direct Routing requires SBC configuration and ongoing management. Without internal expertise, a managed Direct Routing service handles that, though it adds a partner dependency.
A user's mobile SIM number becomes their Teams Phone number. The same number rings across the native mobile dialer and the Teams app, with calls, presence, voicemail, and call history kept in sync.
This option suits organizations with field-based or mobile-first employees where a desk phone is not part of the workflow. Carrier availability is still limited. In the UK, providers including Vodafone and Virgin Media O2 Business now deliver this integration, which signals that momentum is building. Fewer than 5% of Teams Phone customers are currently using it. For most enterprise deployments right now, it is worth understanding but not a primary planning consideration.
No single model covers every scenario for an organization with global users.
The most common pattern among enterprise customers today: Operator Connect for high-volume countries where the carrier has strong coverage and provisioning needs to move fast; Direct Routing for countries outside the operator's footprint, for legacy system integration, or for sites where compliance requirements dictate on-premises connectivity. Teams Phone Mobile layered in for specific user populations if the carrier supports it.
Before settling on an architecture, map out three things: where your users are and whether potential carriers cover those locations, what existing infrastructure and carrier contracts need to be accommodated, and whether any sites have regulatory requirements that affect call routing or data handling.
Pure IP is a Microsoft-certified Operator Connect partner with PSTN coverage across more than 50 countries. We also deliver Direct Routing as a managed service, which means organizations working through a global Teams Phone migration can run both connectivity models through a single provider — one contract, one support relationship, one set of reporting.
We have helped enterprises with complex multi-country migrations design architectures that combine Operator Connect for core markets with managed Direct Routing for coverage gaps and legacy integrations. If you are at the point of mapping out which model applies where, we can work through that with you and flag issues before they slow down deployment.
Talk to the Pure IP team about your Teams Phone migration.