If your business runs an on-site phone system (a PBX), there’s a good chance it’s connected using ISDN lines. Those lines are being retired — here’s what that means and, importantly, why it doesn’t have to mean replacing everything.
What is ISDN, and why is it going?
ISDN is a digital phone line technology that’s carried business phone systems for years, usually with several channels for multiple simultaneous calls. Like the older PSTN network, it’s legacy technology being withdrawn as Ireland moves to all-IP. New ISDN lines are no longer sold, and existing ones are being phased out. For the bigger picture, see the PSTN/ISDN switch-off guide.
The good news: you may be able to keep your phone system
Many businesses assume the switch-off means buying a whole new system. Often it doesn’t. If your PBX is in good shape, SIP trunks replace the ISDN lines with an internet-based connection — you keep the phone system your team knows, cut your call costs, and you’re future-proofed. It’s frequently the cheapest, least disruptive route.
When it’s better to move to the cloud
If your PBX is genuinely near end-of-life, it can make more sense to move to a modern Cloud PBX or VoIP phone lines instead — more features, no on-site hardware, and lower running costs. Not sure which camp you’re in? See when to replace an old PBX.
What to do now
- Confirm whether your lines are ISDN (ask your provider, or ask us).
- Get an honest recommendation: SIP trunks to keep your system, or a move to the cloud.
- Plan the switch early so there’s no downtime — and your numbers come with you.
Running an ISDN phone system? Get a free review and we’ll tell you the simplest way to modernise it.