- PSTN stands for Public Switched Telephone Network, the analogue circuit-switched system that has carried UK voice calls since the era of manual exchanges.
- Openreach is retiring the PSTN and moving all voice services to internet protocol, with the all-IP migration completing in 2027.
- The PSTN works by establishing a dedicated electrical circuit between two callers for the duration of a call, a method known as circuit switching.
- Much of the underlying exchange equipment is decades old, with spare parts and specialist engineering skills becoming harder to source each year.
- Ofcom oversees the migration and sets protections for customers, while the decision to retire the network was taken by the telecoms industry.
PSTN is the analogue Public Switched Telephone Network that has carried UK calls for over a century. It is being switched off because the ageing copper infrastructure is costly to maintain, with digital voice over broadband replacing it by 2027.
Last reviewed: June 2026
What PSTN means and where it came from
Long before the internet, every telephone call in Britain depended on a physical electrical connection between two handsets. That system is the Public Switched Telephone Network, almost always abbreviated to PSTN. Its origins lie in the manual switchboards of the late nineteenth century, where operators physically connected calls by plugging cables into a board. Over the following decades the manual exchanges were replaced by electromechanical and then electronic switching, but the fundamental design remained the same: a network that sets up a dedicated path for each call.
For most of the twentieth century the PSTN was a marvel of engineering and the backbone of national communication. It carried not only voice but, in later years, dial-up internet, fax traffic and a range of monitoring and alarm services. That very ubiquity is part of why retiring it is such a significant undertaking, because so many devices and habits were built around the assumption that a copper phone line would always be there.
The reach of the network also shaped national habits. Cash machines, retail payment terminals, alarm panels and healthcare pendants were all designed around the assumption that a copper line would always be present and would carry a little power of its own. As a result the PSTN ended up supporting services its original designers never imagined, from monitored security to remote meter reading. That breadth is exactly why retiring it touches so much more than the household telephone, and why the migration has to be handled methodically rather than flicked off like a single switch.
How the PSTN actually works
The defining feature of the PSTN is circuit switching. When a call is placed, the network finds and reserves a continuous electrical path between the two parties and holds that path open until the call ends. This dedicated circuit guarantees a steady connection for the duration of the conversation, but it is also inefficient, because the circuit is reserved even during silences and cannot be shared with other calls.
Power is another distinctive feature. A traditional analogue line carries a small voltage from the exchange itself, which is why a corded landline phone could keep working during a household power cut. That characteristic shaped decades of expectations about reliability, and it is one of the reasons the migration to broadband-based voice has required careful planning around back-up power for vulnerable users and critical devices.
Numbering and routing on the PSTN were handled by the exchanges themselves, which interpreted the dialled digits and stepped the call towards its destination across a hierarchy of local, trunk and international switches. This worked reliably for ordinary voice calls but offered little flexibility. Moving a number to a new premises, splitting calls across sites, or adding features meant physical changes in the network. Internet-based voice removes those constraints because the intelligence sits in software, which is one of the practical reasons the industry has been keen to migrate away from the fixed logic of the legacy switches.
Why the analogue network is now obsolete
The PSTN was designed for a single purpose, analogue voice, in a world without data networks. Modern broadband can carry voice, video and data simultaneously over the same connection far more efficiently than a circuit-switched network ever could. Maintaining two parallel national networks, one purely for legacy voice, no longer makes economic or engineering sense when the newer technology can do everything the old one did and more.
The components inside many exchanges are obsolete by any modern standard. Manufacturers stopped producing much of the original equipment years ago, so spare parts increasingly come from cannibalised stock. The engineers who understand the older systems are reaching retirement, and few new entrants are trained on technology that is being withdrawn. Each of these pressures raises the cost and risk of keeping the PSTN running.
There is a customer experience dimension too. As the analogue base shrinks, faults on the old network can take longer to resolve and the pool of compatible replacement equipment narrows. Newer broadband-based services, by contrast, benefit from continued investment and from the same engineering effort that underpins the rest of the internet. Concentrating on a single modern platform allows providers to deliver clearer calls, quicker fault resolution and richer features than the ageing circuit-switched design could ever support.
The cost of keeping ageing infrastructure alive
Running an end-of-life network is expensive in ways that are not always visible to the public. Faults become harder to fix when parts are scarce, restoration times lengthen, and the specialist labour required commands a premium. As more customers move to fibre broadband, the per-line cost of supporting the dwindling number of analogue services rises, because the fixed overheads of the network are spread across fewer users. These mounting costs and reliability risks are central to the industry case for retiring the PSTN rather than patching it indefinitely.
There is also an opportunity cost. Investment and engineering attention spent propping up legacy copper is investment not spent on the fibre and IP networks that will serve the country for decades to come. Consolidating onto a single modern platform allows that effort to be focused where it delivers the most long-term value.
PSTN versus VoIP at a glance
The replacement for the PSTN is Voice over Internet Protocol, or VoIP, which carries calls as packets of data over a broadband connection rather than over a reserved electrical circuit. The table below summarises the main technical differences between the two approaches.
| Feature | PSTN (analogue) | VoIP (digital voice) |
|---|---|---|
| Switching method | Circuit switching, dedicated path per call | Packet switching over the internet |
| Underlying medium | Copper lines and exchanges | Broadband connection |
| Power during outage | Line powered from the exchange | Depends on mains power and back-up battery |
| Efficiency | Circuit reserved even in silence | Bandwidth shared across services |
The Ofcom and Openreach position
Openreach, as the operator of the access network in most of the country, has confirmed that the PSTN will be withdrawn and that the all-IP migration is due to complete in 2027. The company has been moving exchange areas through stop-sell, where new analogue lines can no longer be ordered, followed by the managed migration of existing customers onto digital voice. The retirement is an industry-led decision rather than a legal requirement set by Parliament.
Ofcom's role is to oversee how the migration is conducted and to ensure customers are protected. That includes setting expectations around clear communication, reasonable notice, and safeguards for people who rely solely on a landline or use telecare services. The result is a coordinated programme in which the network operator manages the technical withdrawal while the regulator guards the interests of consumers, and individual communications providers handle the relationship with each customer.
Frequently Asked Questions
What does PSTN stand for?
PSTN stands for Public Switched Telephone Network. It is the analogue, circuit-switched telephone system that has carried voice calls in the United Kingdom since the era of manual telephone exchanges. The term distinguishes the traditional copper network from newer internet-based voice services.
How does the PSTN work?
The PSTN uses circuit switching, which means it reserves a dedicated electrical path between two callers for the whole duration of a call. The connection runs over copper lines and through telephone exchanges. A traditional analogue line is also powered from the exchange, allowing a corded phone to work during a domestic power cut.
Why is BT switching off the PSTN?
The PSTN relies on ageing equipment that is costly to maintain, with spare parts and specialist engineers becoming scarce. Modern broadband can carry voice more efficiently over a single network. The telecoms industry decided to retire the legacy network rather than continue maintaining it alongside fibre infrastructure.
Is the PSTN switch-off happening everywhere at once?
No, the migration is being carried out in stages across the country rather than as a single nationwide event. Exchange areas move through stop-sell and then managed migration at different times. The overall all-IP migration is due to complete in 2027.
What will replace PSTN?
The PSTN is being replaced by digital voice, delivered using Voice over Internet Protocol over a broadband connection. Calls travel as data packets rather than over a reserved circuit. For most users the phone number stays the same, while the handset is generally connected to the broadband router.
