| Feature | VoIP | ISDN |
|---|---|---|
| Technology | Calls over your internet connection. | Digital calls over dedicated copper lines. |
| Future | The UK standard going forward. | Being withdrawn — the UK switch-off is underway. |
| Line rental | None — no physical phone lines needed. | Per-channel rental on every line. |
| Call costs | Low-cost or inclusive UK calls. | Higher per-minute call charges. |
| Flexibility | Add users in minutes; work from anywhere. | Fixed channels; engineer visits to change. |
| Features | Call routing, apps, voicemail-to-email, analytics built in. | Basic calling; extras cost more. |
| Number portability | Keep your numbers, use them anywhere. | Numbers tied to lines and locations. |
Choose VoIP if…
- You want out before the switch-off deadline
- You want lower bills and inclusive calls
- Your team works across sites or from mobiles
Choose ISDN if…
- Honestly — there's no good reason to stay on ISDN
- Legacy equipment is the only thing holding you
- You're contractually stuck (we can review that)
Our verdict
This one isn't a close contest. ISDN is being switched off across the UK, so every ISDN business will move — the only question is whether you move on your own timetable or in a last-minute rush. Moving early to VoIP cuts costs immediately, keeps your numbers, and gets migration done calmly. We handle the whole switch, including porting, with no downtime.
Frequently asked questions
When is ISDN being switched off?
The UK's ISDN and PSTN networks are being withdrawn, with services progressively unavailable to order and full withdrawal following. If you're still on ISDN, you need a migration plan now rather than later.
Will I lose my phone numbers moving off ISDN?
No. We port your existing numbers to VoIP so customers dial exactly the same numbers as before.
Is VoIP call quality as good as ISDN?
On a decent business connection, yes — typically better. HD voice on VoIP is clearer than ISDN, and we check your connection first so quality is guaranteed.
What happens to my alarm lines, card machines and lifts?
Anything running over old lines needs checking — many devices need an upgrade or an alternative. We audit all of it as part of migration so nothing gets missed.
Not sure which is right for you?
Tell us how your business works and we'll recommend the best fit — no hard sell, honest UK advice.