In this article we outline the purpose of the public switched telephone network, its impending closure and what action you need to take now to prepare for this.

Published 27 November 2020

Last updated 1 December 2020

In 1891 an American undertaker named Almon Brown Strowger noticed that he was losing business to his competitor. After discovering that the local telephone switchboard operator happened to be the rival undertaker’s wife, he realised that when callers were asking to be connected to ‘the undertaker’, she was favouring her husband’s business over Strowger’s.

In response to this he invented the first automatic telephone exchange, taking his rival’s wife out of the equation and permanently transforming voice communication.

His invention – the public switched telephone network (PSTN) – gives us the ability to dial a unique number and be automatically connected to people anywhere in the world. The world is now covered in a mesh of wires, undersea cables and satellites, with cabinets and poles on every street and countless buildings housing large ‘public switching exchanges’. It is one of mankind’s greatest inventions, transforming society on many levels by revolutionising telecommunications.

Despite its enormous impact on the world, the PSTN is closing on 31 December 2025. The majority of organisations need to take action now to prepare for this. The potential impact of inaction could be serious, and in some circumstances, possibly fatal.

If this is such a crucial network, why close it?

The PSTN has developed and extended since its inception, accommodating a huge growth in the number of users and exploiting new technologies to allow for faster connections, as well as reduced operational costs to ensure economic viability.

While it has evolved, the world has also changed dramatically since 1891. Telecommunication now primarily uses data-based services, rather than traditional voice calls.

As a result, the PSTN in its current state as a dedicated voice transport network will close at the end of 2025. It will migrate to the internet, where it will be delivered alongside video and data-based services.

Why is this an improvement?

Services we now regard as commonplace such as video calling and instant messaging all require multimedia delivery at very high speed.

The legacy PSTN technology was never designed to manage the speed or the integrated signalling systems to carry all 3 media (voice, video and data), and so it is no longer fit for purpose. These services will be combined and delivered to homes and businesses through a single connection.

The closure

Network operators BT, Virgin Media and KCOM currently maintain both the PSTN and the internet in parallel to deliver public switched services.

This is not financially viable for the network operators, or for the manufacturers of the hardware, who from December will stop supporting the legacy technology. This means that if faults occur, they may not be repairable.

What does this mean for public sector organisations?

Many organisations already use the internet for voice calls, known as Voice over Internet Protocol (VoIP), and it is possible to convert existing phone equipment from traditional phone lines to VoIP connections. Alternatively, the hardware can be replaced with IP-ready equipment.

Migrating voice telephony services is relatively straightforward, but there is a fundamental difference between the old and new phone lines that you need to be aware of. Namely, that the PSTN delivers voltage from the network to power end devices, while the internet relies on local power. A traditional landline phone does not need to be plugged in to the mains – it gets its power from the phone line itself. In comparison, a VoIP phone needs power from the mains, in addition to an internet connection. That is something you need to plan for.

Is there more to it than switching out or converting phones?

Many other services rely on PSTN, including emergency phones in lifts, traffic lights, railway signals, personal alarms and motorway signage.

All of these services are dependent on the voltage supplied by the PSTN, and all will need local batteries in addition to an internet connection once the network closes, with some requiring more complex solutions. For such critical services, it is easy to imagine the impact a flat battery could have on transport links and personal safety.

Is support available for this transition?

We are working closely with Openreach to ensure that public sector organisations are aware of how the PSTN closure may affect them and what support is available.

Openreach is leading on this migration as BT Group, which has in its various forms provided PSTN services to residential and business customers for over 100 years.

The task is complicated because although BT are aware who they have sold an analogue voice line to, they don’t necessarily know what it’s being used for – particularly when sold on a wholesale level.

Organisations, therefore, need to assess their telecoms estate to understand what PSTN-reliant technology they may have that needs modifying or upgrading, and put a plan in place to complete this switch.

Please contact Phil Laws at Openreach to discuss any services you have that may be impacted by the closure of PSTN by emailing