PSTN Replacement and Copper Switch-Off

C3ntro Global

September 28, 2026

PSTN replacement is the process of moving voice services off the legacy copper telephone network and onto virtual numbering, typically through SIP trunking or DID (Direct Inward Dialing) infrastructure. It matters right now because the deadline is no longer theoretical. In the United Kingdom, Openreach has confirmed the copper network closes on January 31, 2027, with no further extension. In the United States, AT&T has committed to retiring the large majority of its legacy copper by the end of 2029 and has already stopped accepting new copper orders across most of its footprint. For any business, carrier, or platform still running voice over PSTN circuits, the window to migrate without disruption is measured in months, not years.

Which markets are switching off copper?

Market	Deadline	Status	What's Still Exposed
United Kingdom (Openreach)	January 31, 2027	Fixed, no further extension	~1.5M lines, ~350K business premises (mid-2026)
United States (AT&T)	End of 2029 (bulk of legacy copper)	Rolling, region by region, FCC-approved	As little as 90 days' notice per wire center

The United Kingdom is the clearest case. Openreach pushed the original December 2025 deadline back to January 31, 2027 to give providers more time to migrate vulnerable and elderly customers safely, and has since made clear the new date will not move again. As of mid-2026, roughly 1.5 million lines were still running on the old network, including close to 350,000 business premises, according to Openreach’s own reporting.

In the United States, the picture is more gradual but just as firm. AT&T has FCC approval to discontinue copper service across hundreds of wire centers and is working region by region toward a 2029 target for the bulk of its legacy network, citing the cost of maintaining aging copper infrastructure. Other US carriers are watching closely, and regulatory changes at the FCC in 2026 have made it easier for operators to file for copper discontinuation faster than before.

Beyond these two markets, the direction is consistent across most developed telecom markets: copper is being phased out in favor of IP based voice, and providers that depend on PSTN connectivity for numbering, call termination, or PBX integration are the ones most exposed.

What breaks if you wait?

The risk is not just “the phone stops working.” When a copper line is retired, everything riding on it goes down at the same time: voice service, but also alarm systems, payment terminals, elevator lines, telecare devices, and any legacy PBX or ISDN trunk still in place. For a CPaaS platform, wholesale carrier, or UCaaS provider, the real exposure is at the number level. A DID that was never properly ported or re-provisioned before a cutoff date can simply stop routing, taking a client’s inbound calls with it.

There’s also a cost dimension. As carriers wind down copper, remaining customers on legacy lines often face rising premiums for a service that is actively being phased out, which makes waiting more expensive, not less. And because copper retirement in the US now moves on a rolling, region by region basis, a business can receive as little as 90 days’ notice before a specific wire center goes dark. Migrations planned in advance are simple. Migrations forced by a shutoff notice rarely are.

Why is this the right moment to move?

The infrastructure to replace PSTN at scale already exists and is growing fast. The global SIP trunking market, the technology layer that carries voice traffic once copper is gone, is projected to grow from about $85 billion in 2026 to more than $181 billion by 2031, according to industry research published this year. That growth reflects a broader shift: cloud communications platforms, contact centers, and enterprise voice systems are already built around IP based numbering, not legacy circuits. Migrating now means moving onto infrastructure that is maturing, not onto something still being proven.

What Are the Five Steps of a PSTN Migration That Doesn't Drop a Number?

Audit every number and every dependency. Before touching anything, map which numbers are active, which systems depend on them (voice, SMS, alarms, fax, IVR), and which are tied to a specific copper circuit versus a portable DID. Numbers with no clear owner are the ones most likely to get lost mid migration.
Choose a numbering partner with real multi country coverage. A migration that only solves for one market creates the same problem again the next time a region shuts down copper. Working with a wholesale DID provider that covers 120+ countries means numbers can be re-provisioned once, on infrastructure designed to scale internationally, instead of repeating the process market by market.
Port before you cut, never after. Numbers should be fully ported and tested on the new SIP trunking or DID infrastructure while the old copper line is still active. Running both in parallel, even briefly, is what prevents a dropped call becoming a dropped customer.
Provision with redundancy, not just replacement. A rushed migration that swaps one single point of failure for another has not actually reduced risk. Providers with fast, self-managed provisioning let a business set up backup routing and failover paths during the cutover window itself, rather than after something breaks.
Validate, then decommission. Only after inbound and outbound traffic has been confirmed on the new numbering setup, across every dependent system, should the old copper line be formally closed. Skipping this step is the most common reason migrations that looked complete on paper still cause an outage.

Choosing a Partner for the Migration

None of these five steps matter much if the underlying provider can’t move at the same pace the deadline demands. That’s where the difference between numbering providers actually shows up: how fast a new DID can be provisioned, how many countries are genuinely covered rather than resold through a third party, and how much of the process a client can manage themselves through a self service portal instead of opening a ticket and waiting.

C3ntro Global has spent more than 30 years in this sector, and PSTN replacement is one of the areas where that experience shows most directly, because a rushed number migration exposes gaps that a stable, established carrier simply doesn’t have. Coverage in DIDs across 120+ countries, and 46 with PSTN Replacement, rapid activation, and a single carrier relationship instead of juggling multiple regional vendors are what make a copper switch-off deadline manageable instead of stressful. It’s part of why, inside the industry, C3ntro keeps getting referred to as the DID experts.

The copper network is closing on a fixed timeline in more than one major market at once. The businesses that migrate on their own schedule, with a clear five step plan and a partner that can execute it globally, are the ones that will never notice the deadline at all.

The Technical Layer: API Provisioning and Real-Time Control

At enterprise scale, manual DID provisioning is not a viable operating model. The API layer is where the operational capability of a wholesale DID provider becomes visible or invisible to the customer. C3ntro Global’s provisioning platform is built around the expectation that operators, CPaaS companies, and enterprise teams need to move fast without depending on a human in the loop at every step.

What the Platform Enables

Real-time inventory search by country, area code, format type, and compliance status
Instant number assignment with routing configuration in the same API call, no manual review step between order and activation
Automated compliance documentation retrieval per number, so the paper trail exists at provisioning time, not during an audit
Live inventory status across the full DID portfolio, with no need for manual queries to understand what is active, pending, or available
Webhook-based event reporting for number status changes, porting progress, and routing updates

This distinction, between headline coverage and operational depth, is what determines whether a provisioning request succeeds on the first attempt or triggers a support escalation three weeks into a deployment.

Where DID Expertise Connects to the Broader Stack

DID numbers do not exist in isolation. They are the addressing layer for everything that happens in a voice or messaging deployment. Understanding DIDs at the expert level means understanding how they connect to SIP trunking, how they interact with SMS enablement, how they behave across different contact center architectures, and how compliance at the number level affects every communication that flows through it.

C3ntro Global’s DID infrastructure is part of a wider wholesale platform that includes voice termination and A2P SMS. That integration is not a product bundle. It is an architectural reality: the same carrier relationships that give us DID depth in a market also give us voice termination quality and SMS routing reliability in that same market. The expertise transfers across services because the foundation is the same.

For more on how each service layer works, see How the Wholesale DID Market Works, How Do DIDs Work?, and What Is a DID Number?

Frequently Asked Questions

What is PSTN replacement?

PSTN replacement is the shift from voice service delivered over the legacy copper telephone network to voice delivered over IP, typically through SIP trunking connected to DID (Direct Inward Dialing) numbers. The number stays the same for the end user; what changes is the infrastructure carrying the call.

When do copper networks switch off in the UK and US?

In the United Kingdom, Openreach has set January 31, 2027 as the final cutoff for all services running on its copper network, with no further extension planned. In the United States, AT&T is retiring the large majority of its legacy copper by the end of 2029, on a rolling, region by region basis rather than a single national date.

Does my phone number change when I migrate off PSTN?

No, a properly planned migration ports the existing number onto SIP trunking or DID infrastructure before the copper line is cut, so callers keep dialing the same number. Numbers only get lost when porting happens after a line is already retired, or when ownership of a number was never clearly tracked.

How long does a PSTN to SIP or DID migration take?

It depends on how many numbers and dependent systems are involved, but the five step process, audit, choose a partner, port before cutting, add redundancy, then validate, is designed to run in parallel with the existing copper line so there is no forced downtime window. Starting months before a regional deadline, rath

PSTN Replacement and Copper Switch-Off

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