The UK PSTN hard cutoff is January 31, 2027. For enterprises still running legacy PBX or ISDN infrastructure in the UK, the Teams Phone migration is no longer a choice sitting on an internal IT roadmap. The deadline is set by infrastructure withdrawal, not by the project calendar.
Germany, Japan, and Australia are running their own switch-off programs on parallel timelines. Any multinational with sites in more than one of these markets faces compounding deadlines across geographies.
The content around Teams Phone migration frames it as a strategic decision. But for enterprises in these markets, the frame no longer fits. The infrastructure they've been running voice on is being withdrawn and that changes the timelines.
What the PSTN switch-off means for enterprise voice
The Public Switched Telephone Network (PSTN) is the copper-wire infrastructure that has carried enterprise voice calls for decades. BT is decommissioning it. The final cut in the UK is January 31, 2027.
After that date, any business phone system still connected to the PSTN will stop working. That includes legacy PBX systems running over ISDN circuits. It includes analog devices connected through copper lines. It includes the direct dial numbers that have been on those lines for years.
Teams Phone itself is unaffected by the switch-off. The legacy infrastructure enterprises run alongside it is what's being withdrawn. For organizations that have already migrated voice to Teams Phone, this is background noise. For organizations that haven't, it is a hard stop.
Which markets are affected and when
The UK has the most immediate confirmed deadline for most European enterprise IT teams. BT's Openreach network reaches the hard cutoff on January 31, 2027. The current period is the final migration window. Migration service demand is increasing, and porting queues are lengthening as the date approaches.
The Netherlands and Estonia have already completed their switch-offs. Germany, Japan, and Australia are following the same pattern on their own schedules. The progression is consistent: a stop-sell phase, a mass migration period, then a hard cutoff.
For a multinational enterprise, the relevant question is not whether the switch-off is happening. It is how many of the organization's sites are in affected markets, and whether those sites have been mapped against the relevant deadlines.
Why the migration window is shorter than it looks
"We have until January 2027" is the wrong frame. The usable runway is shorter than the calendar suggests, for two reasons.
First, infrastructure work takes time. The steps before go-live — connectivity model selection, number porting, SBC setup if Direct Routing is in the mix, network readiness validation — none of them complete in days. For a complex multinational deployment, the full process takes months. Enterprises that start in Q4 2026 will be competing for porting capacity with every other organization that also waited.
Second, discovery takes longer than expected. Most IT teams inherit phone environments they didn't build. The actual inventory of numbers, lines, analog devices, and carrier contracts is rarely documented accurately. A German insurance company working with Pure IP on a Teams Phone assessment found tens of thousands of DDI numbers they hadn't accounted for. Excess PSTN connectivity was identified during that process too. Rationalization work like that adds weeks to any migration schedule.
What Teams Phone infrastructure work takes the most time
Number porting is the most common bottleneck. Carriers impose porting windows. Some markets have regulatory requirements that add steps to the process. As deadline pressure builds across a market, porting queues lengthen. Enterprises at the back of a porting queue in the final months before a cutoff have limited recourse.
Network readiness assessment comes second. Teams Phone voice traffic has specific requirements around latency, jitter, and packet loss. A network that handles video calls acceptably may still produce poor call quality at enterprise telephony volume. Validating network performance before go-live is the step that compressed timelines tend to skip. It tends to reappear as a support problem after go-live.
For deployments using Direct Routing, SBC configuration adds further lead time. In markets where Operator Connect doesn't have full PSTN coverage, Direct Routing fills the gap. Setting up and testing a managed SBC requires configuration, certificate setup, and call flow testing before going live, even with a managed provider.
Where enterprises in switch-off markets should start
An accurate inventory of what's connected to the PSTN is the starting point. Not a theoretical list of what should be there, but a line-level audit of what is: every DDI, every analog device, every carrier contract with its porting timeline. Organizations consistently find more than they expected when they do this properly.
From there, the connectivity model question becomes answerable. Operator Connect works for markets where the provider has full PSTN coverage and provisioning can happen through the Teams Admin Center. Direct Routing covers markets outside that footprint and sites with legacy infrastructure requirements. Most enterprise deployments use both.
Pure IP provides Operator Connect coverage in 50+ countries and delivers managed Direct Routing for markets where that footprint has gaps. Enterprises assessing where they stand against their switch-off deadline can work through the discovery process with Pure IP's team before any provisioning decisions are made.
The window is not closed. But organizations still treating Teams Phone as a project for next year are, in several markets, already running late.
Frequently asked questions
When is the UK PSTN switch-off deadline?
January 31, 2027. BT and Openreach have confirmed this as the hard cutoff with no planned extension. The current period is the final migration window for businesses still on analogue or ISDN lines.
Do I need to move to Teams Phone before the PSTN switch-off?
Not specifically Teams Phone, but you do need to move to an IP-based voice solution before your market's cutoff date. Teams Phone is one option. The underlying requirement is disconnecting from PSTN-connected infrastructure before the deadline. Enterprises already using Teams for collaboration are practical candidates for Teams Phone migration, since the platform and licensing may already be in place.
How much time does a Teams Phone migration take before the deadline?
It depends on the environment. For a single-market deployment with a clean number inventory and a provider already certified for Operator Connect, provisioning can move quickly. For multinational environments with legacy PBX coexistence and number porting across multiple carriers, the process can take several months. Sites in markets where Direct Routing is required add further lead time. Most Teams Phone infrastructure deployments benefit from a 12 to 16 week lead time minimum, covering discovery, provisioning, and testing. In high-demand migration periods, porting timelines extend further.
