ISDN switch-off: replacing ISDN2 and ISDN30 lines

ISDN is being retired along with the PSTN. If your phone system connects through ISDN2 or ISDN30, you need a replacement before your lines stop working.

By the Alltone Telecoms team. Updated 24 October 2026. About 2 minutes to read.

Your three options

SIP trunks: keep your on-site PBX and replace the ISDN lines with internet connections
Cloud phone system: replace the PBX and lines with a hosted VoIP system
Microsoft Teams calling: make Teams your phone system

Keeping your DDI ranges

ISDN30 customers often have ranges of direct dial numbers. These can be ported as a range to SIP or cloud VoIP so every extension keeps its direct number.

Connectivity

Replacing 30 ISDN channels with SIP needs roughly 3 Mbps of symmetrical bandwidth with headroom. Many sites with heavy call volumes choose a leased line or a dedicated voice connection.

Common questions

Something else on your mind? Call 020 7112 8558 or send us a message and a telecoms specialist will reply.

Can my old PBX work with SIP?

Many PBX systems from the last decade can, sometimes with a licence or a gateway. Older systems are usually cheaper to replace with cloud VoIP.

Talk to a telecoms specialist

Tell us how your business takes calls today and we will recommend a setup, with a clear monthly price. Most quotes are ready the same day.

UK-based support team
Free setup and number porting on most plans
Monthly rolling options available
No obligation quote

Prefer to talk? Call 020 7112 8558, Monday to Friday, 9am to 5.30pm.

Call us Get a quote