What is the PSTN & ISDN Switch Off?

Openreach announced in 2017 that the PSTN (Public Switched Telephone Network) system is ageing and will reach its end-of-life by December 2025. In May 2024, they extended this deadline to 31st January 2027. From this point onwards, all businesses will need to have upgraded to a VoIP (Voice over Internet Protocol) phone system to be able to continue making calls, and upgraded any services which use analogue lines.

Though January 2027 is the final ‘switch off’ deadline, PSTN and ISDN services are being withdrawn across the country in phases, meaning this could impact you earlier than you expect. All new installations of PSTN and ISDN will be stopped from September 2023, and this includes adding additional lines to an existing PSTN / ISDN service.

What is the PSTN & ISDN
The Public Switched

What is PSTN & ISDN?

The Public Switched Telephone Network (PSTN) is what most would class as a traditional telephone line. It’s an old technology, using the same setup as the first phone network from the 1800s. It’s become increasingly costly to maintain and run, and needs replacing with more modern technology that is suitable for the world we live and work in today.

ISDN (Integrated Services Digital Network) was introduced in 1986, and while using the PSTN circuits, has allowed the digital transmission of voice calls, video calls and other data services simultaneously. It has become a more expensive network to maintain, and with it using the PSTN circuit, will also reach its end-of-life in 2027.

What is replacing PSTN & ISDN?

VoIP is the next generation for the country’s telephone network. By January 2027, all businesses will need to upgrade their landline to a VoIP (Voice over Internet Protocol) phone system to continue making and receiving calls.

This switch off doesn’t only affect phone systems. Any fax machines, alarms, CCTV systems, payment terminals, door-entry systems, information displays and emergency phones that currently use the older PSTN circuit will need to be updated by January 2027 too.

Customers will also need to upgrade their broadband to either FTTP (Fibre to the Premises) or a new broadband product called SOGEA (Single Order Generic Ethernet Access), which provides the ability to have broadband without a phone line.

What is replacing
What is Voip

What is VoIP?

VoIP (Voice over Internet Protocol) provides the ability to make and receive calls over an internet connection. It converts the voice communication into digital data that travels across the internet to its recipient.

VoIP allows calls to be made on any device that has a reliable internet connection, including smartphones and laptops. A VoIP phone system is much more flexible, as they can be provisioned remotely, meaning you can add additional lines to the system easily. Call costs via VoIP are much cheaper when compared to traditional phone systems and usually come with innovative features.

Benefits of VoIP

Cost Effective

Call costs on a VoIP phone system are significantly cheaper compared to traditional phone systems. The phone system is much easier and quicker to set up too, which means you could save on engineering fees.


As they are cloud-based, VoIP phone systems are easier to scale, meaning you can add additional handsets as your business grows.


With the rise of remote/hybrid working, a VoIP phone system allows you to be more flexible with where you are working, while still always remaining connected.

Business Improving Software

VoIP phone systems come with the ability to add a wide range of cloud-based services that can help to improve your business, including software such as Call Recording and On Hold Marketing.

Increased Call Quality

As VoIP phone systems use your internet connection, the call quality on phone calls is much higher than systems still using an older network. The reliability of this connection is also much better.

Modern Phone Features

VoIP deskphones come with a wider range of phone features as standard, including video calling, Presence status, voicemails to email and easy-to-use call settings when needing to manage calls.

Get ahead of the telecoms switch off and upgrade to a VoIP phone system today!

Find out how we can help upgrade your business to VoIP by completing the details below:

  • * Required fields

  • Hidden
    MM slash DD slash YYYY
  • Hidden
  • This field is for validation purposes and should be left unchanged.

FAQs Answers to some common questions…

A VoIP phone is just like any other traditional deskphone and will normally operate in the same way. The key difference is how your phone calls travel across the network; with VoIP this is done via an internet connection instead of the traditional Public Switched Telephone Network (PSTN). VoIP phones will often have a greater array of functionality than their traditional counterparts.

Yes, it is possible to keep your existing business phone number when you make the switch to VoIP – this process is done between phone providers, so we’ll take care of everything for you.

SIP stands for ‘Session Initiation Protocol’, and SIP trunking is essentially the protocol which allows telephone systems to communicate within a network via an internet connection, rather than traditional phone lines. SIP allows VoIP calls to commence within businesses, as it begins the process which allows voice and other data to be transmitted between devices.

VoIP call charges will vary from one provider to another, but long-distance calls are usually far cheaper on VoIP networks than on the PSTN.

The quality of a VoIP call is the same, if not better, than that through traditional phone lines. VoIP simply requires a reliable internet connection to maintain call quality, which is something that will be assessed by our 4Com experts if you choose to have the system fitted.