The ISDN switch-off: is your business ready?

When you consider that BT and KCOM have been operating our telecom services since 1846 and 1899 respectively, their recent decision to switch off old-style phone networks by 2025 is a truly historic milestone.

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According to the announcement, both companies will begin phasing out PSTN and ISDN services in 2020. In fact, they’ve already begun the big switchover. Any company still using old technology needs to sit up and listen.


The Public Switched Telephone Network is the system of wires and exchanges that have been in use for 100 years. It was developed to carry voice signals as an analogue wave-form.

ISDN is a technology that was developed so that sound could be transmitted in digital packets, but it still depended on the same analogue wired network. Nevertheless, ISDN made it possible to send several audio, video and other signals across a wire simultaneously, and therefore radically increased the network’s capacity.

However, both of these technologies have been outstripped in their carrying potential by the infrastructures now in place to carry internet traffic, so a radical transition has become inevitable.

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Cloud-based VoIP phone systems can be buggy to set up, but they bring with them a host of useful new features. It makes no sense to put off the switch until the last minute. You need to look into VoIP today (see

Who is affected?

Eventually, this will affect everyone. A survey by OFCOM in 2017 found that two million British businesses were still dependent on old ISDN phone services. A quarter of them didn’t even know that change would soon be upon them.

How does it work?

The new phone systems depend on SIP (Session Initiation Protocol) to create their connections, and VoIP (Voice over Internet Protocol) to encode/decode the signals that cross it. A wholesale VoIP termination provider negotiates the transactions between the several different telecom and internet companies involved in routing the call. For more information, see

If you already have an internet connection, the calls you make are technically free regardless of the distance between the caller and the recipient. However, leased equipment, increased broadband capacity, network services and technical support will keep telecom companies in business, but in changed forms. You should be looking at your new options as soon as possible.

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