What is PSTN and why is it being switched off?

You might have heard that BT Openreach are switching off the Public Switch Telephone Network (PSTN) in December 2025 and a lot of people don’t realise that it could affect them. You may think the PSTN is only going to affect just phones, but ANY equipment that uses it will stop working. That can range from alarms, to CCTV, to EPOS machines, to door systems… it’ll even affect fax machines, so you best tell your grandad!

What is PSTN?

PSTN relies on a network of copper cabling, no internet connection required – in fact it doesn’t even need power, so keeps running even during power cuts. Sounds great, doesn’t it? Well, originally it required human operators to patch calls through to people; now it uses digital switchboards to do the same thing.

When making a call through PSTN, your phone converts the sound of your voice into electrical signals that travel through the copper wire. That signal goes to a Central Office (CO), that is then sent to one of four ‘gates’:

1. If you’re making a local call, it will go directly from the CO to the recipient.
   
   
2. If you’re making a call to somewhere that is further away, the call will be routed to a Tandem Office, then to your recipient’s CO, then to your recipient.
   
   
3. If you’re in a different county, or another part of the UK entirely, it will first go to a CO, then to a Tandem Office, then to a Toll Office, where the call would be sent to the CO of the recipient.
   
   
4. Then if you’re sending an international call, the call will go through the same gates but as an extra step go to an International Gateway which would connect the call to the recipient.

It might seem like this would take hours, but it happens in a matter of seconds.

Why are we moving away from the PSTN?

Well, the technology is as old as phones are – it’s technology that Queen Victoria could have used! And as we need more and more data to communicate, fibre-optics has become THE option for telecommunication. PSTN struggles with the expectations of 21^st Century communication and has been considered a relic for well over a decade.

With full fibre readily available, dividing our telecoms between PSTN and digital means that maintaining and combining both is more expensive when one easily surpasses the other.

Using Voice over IP (VOIP) – which uses the internet to transfer data – instead of a call being bounced between a series of gates it instead instantly, directly, connects to the recipient.

We break down the switch-off in this video on our YouTube channel.

This is a sneak peek into our YouTube series of explainer videos – with more to follow! We’d really appreciate you checking it out and giving us a like and subscribe 😉

So what should you do?

It’s not all doom and gloom though. The push to upgrade to newer, more capable technology means you’ll be able to do a lot more in the long run and it’ll be much easier to improve things. Moving away from PSTN means you don’t have to worry about setting up landlines anymore – all of your phone systems can operate using your existing internet service.

The biggest issue will be in replacing any older technology you might have that still relies on PSTN, and in fact, knowing what uses it at all.

December 2025 might seem far away, but the sooner you find out what you need to change the better. If you think you’ll need some help moving to an IP network, please get in touch.