PSTN, ISDN, And VoIP: What Exactly Do These Phone Related Acronyms All Mean?

Businesses are all looking to change the way they communicate after Openreach announced that it intended to switch off the traditional fixed phone line system in 2025. However, there are some companies that are still in the dark about what they need to do and are puzzled by the technical jargon. So, what do PSTN, ISDN, and VoIP all mean, and what do they do?

Phone Related Acronyms

What Is The PSTN Network?

What is the PSTN Network

PSTN stands for the Public Switched Telephone Network. It has been around in various forms since the telephone was first used over 100 years ago. It is also known by other names including fixed-line telephones, landlines, and Plain Old Telephone Service.

The PSTN network starts at the local exchanges that are all linked together. A series of copper wires in pairs runs from the exchange to roadside boxes. From there, the wire travels up telephone poles and along to individual houses and businesses.

Many modern houses and buildings have these wires all underground. Most of the PSTN equipment at the exchanges has been unchanged for many years.

This network has seen a large reduction in use in the UK over the past few years. This is one of the reasons why Openreach is switching off the service in 2025.

Another reason is cost. Many of the components needed for the network are no longer manufactured or are expensive to maintain.

What Is The ISDN Network?

What is the ISDN Network

ISDN stands for Integrated Services Digital Network. It uses digital transmissions to send and receive information down traditional copper wires.

It was introduced by BT (British Telecom) in 1986 and gave the old telephone network a new lease of life.

BT replaced the old and outdated phone lines with digital lines so that services such as the internet and video calls were available.

Although it might sound like they do the same thing, the difference between ISN and VoIP which comes later is that ISDN uses copper cables to provide calls and the internet. With VoIP, the calls are made on the digital lines that the internet uses.

What Is VoIP?

What is VoIP

VoIP stands for Voice over Internet Protocol. It has actually been around for a little while, and many companies have already made the switch to VoIP.

The main difference with VoIP is that it doesn’t rely on copper wires to transmit information. It uses the same fiber or mobile signals that the internet uses.

This makes VoIP a good alternative to PSTN as there are no issues with call quality or distance. It is also a safe and secure way to transmit data and personal information, though robust security procedures still apply.

If your business is still using PSTN, then you will need to switch over to VoIP before 2025. Your existing internet service provider may also be able to offer you a VoIP service.


All of the different acronyms that are used can be confusing. However, in just a few years, the old PSTN and ISDN systems will be replaced with VoIP. It is important that you ensure your business is ready for the switch off in 2025.