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ISDN end of life: what it means for your phone system

ISDN gave businesses multiple simultaneous calls over a digital line. It is being retired alongside analogue lines — here's how to plan the replacement.

Blog · Published 21 August 2026

Who still relies on ISDN

ISDN30 typically sits behind an on-premise phone system in offices with a reception desk, a main number and a block of direct dials. ISDN2 tends to serve smaller sites needing a handful of concurrent calls.

If your phone system lives in a cupboard, has a maintenance contract, and nobody knows who set it up, there is a good chance ISDN is feeding it.

What replaces it

The like-for-like replacement is SIP, which delivers the same channels over your internet connection and can usually plug into an existing system. The better long-term answer is a cloud phone system, which removes the on-site hardware entirely.

  • Direct dial numbers port across unchanged
  • Call capacity becomes a setting rather than a physical line count
  • Remote and mobile workers get the same features as the office
  • No maintenance contract on ageing hardware

Timing the move

Number porting takes a couple of weeks and a multi-site estate takes longer. Working back from your renewal date, and allowing time to test call flows, is the difference between a planned project and an emergency.

Want this set up for you?

Plans start at £19 per user per month with UK calls included. See pricing or get a quote.

Related pages

ISDN replacement

Replace ISDN30 and ISDN2 before it's retired.

More about isdn replacement

Business phone systems

A full cloud system for a growing team.

More about business phone systems

Pricing

Plans from £19 per user per month.

More about pricing

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