From phone lines to fibre – how the ISDN switch-off is a significant shift in the way we communicate

by | Feb 6, 2020

Since Victorian times, the UK’s telephone service has utilised copper cables to connect telephones to local exchanges, linked together to create a national telephone network, or PSTN.


Although managed by different providers over the years, this network connected homes and businesses all over the UK for well over 100 years. Not much has changed in that time with the technology and the physical infrastructure has barely changed in the last century.

The parallel development of ISDN, a multi-channel PSTN connection that enabled up to 30 calls on the same line simultaneously, meant businesses could buy telephony services in bulk, and many organisations still do.

The most significant development was in the eighties and nineties with the introduction of DSL technology. This enabled digital data to use the same line as the telephone communication, without interfering with voice calls. This resulted in the wide adoption of DSL Broadband across the UK, breathing new life into the copper lines and local telephone exchanges.

For the last 30 years or so, the situation has remained relatively unchanged. People have continued to buy copper lines under a variety of guises, for their homes and businesses, delivering the same user experience of a phone and broadband plugged into the wall socket.

However, use of the PSTN fixed line telephony network has been rapidly declining, with the amount of time spent making landline calls halving in the last six years alone.

In the summer of 2018, Openreach announced significant changes that would affect the telephony industry.

The voice network was no longer paying for itself as the volume of calls dropped. The cost of maintaining the older technology in telephone exchanges continues to increase and in some cases equipment was so outdated, Openreach no longer offered replacements.

Openreach announced two target milestones to the industry:

  1. From 2023, all PSTN and ISDN voice services would no longer be sold
  2. From 2025, the PSTN and ISDN voice networks would be turned off

All Openreach connections from 2025 will be ‘data only’ – solely broadband. Voice services will only be available as Voice over IP (VoIP) service provider offerings that run over the top.

Many businesses have already made the switch to VoIP, but there are many who still have years left on their ISDN contracts.

Organisations with large and complex telephony estates, especially ones with PSTN setups, need to start planning their migration. It won’t be possible to copy and paste setups using PSTN Multi-Line, diverts and AUX lines into the new world of hosted telephony, so organisations need to break down their requirements and work with suppliers to design new solutions.

If your organisation is still using PSTN or ISDN, now is the time to act. The deadline might seem far away but with such a significant migration, ample time is needed to ensure a smooth transition. The price of voice services is also increasing every year as the deadline looms closer.

We can help you navigate this significant transition with minimal disruption to your business. Contact us today to start your switch.