BT is turning off the PSTN. If your business still has analogue or ISDN lines, they will not work much longer. Openreach has been signalling this for years, pushing dates around, and issuing extensions. The short version: if you have not moved yet, move now. If you have moved badly, fix it now.
What is actually being switched off
The public switched telephone network (PSTN) and ISDN services. That covers analogue lines (the one your alarm panel and door-entry system are on) and ISDN30 trunks (the thing you bought in 2007 for your on-prem PBX).
It does not cover broadband, leased lines, or fibre to the premises. Those keep going. But anything riding on traditional copper voice circuits is affected.
What the options are
There are three paths, in rough order of cost and effort.
Hosted VoIP, standalone. A cloud-hosted PBX from a provider like Gamma, 8x8 or Ringover. Desk phones plug into your network, softphones on laptops, call plans by seat. For sub-30 user businesses, this is often the right fit. From about £10 per user per month.
Microsoft Teams telephony. Teams Phone with direct routing, using your existing Teams tenant as the phone system. You already have Teams, your staff already use it, now it rings. From about £6 per user per month plus call plans. For Microsoft shops, this is usually the right fit.
Cloud PBX from an MSP. We run our own platform, built on Wildix. The pitch for our clients is usability equal to Teams, with a more customer-service-oriented feature set (queue management, wallboards, supervisor breakout). For contact-centre-shaped businesses, often the right fit.
What to actually check before you switch
Your numbers. Geographic numbers, 0800, 0345. All of these can port. Some take two weeks, some take eight. Start early.
Your hardware. Desk phones older than five years are probably not going to be compatible. Budget for replacements. Cordless is more forgiving but the base stations may need replacing too.
Alarm panels, door entry, lift lines, fax machines. All the “special” lines. These need analogue terminal adapters or a standalone SIM-based solution. Do not forget them on migration day.
Network readiness. VoIP quality needs QoS on the network, reasonable bandwidth (rarely the bottleneck), and a properly configured firewall. If any of that is wobbly, fix it first.
Common mistakes we see
Porting numbers on the Friday of a bank holiday. Do it midweek, first thing.
Underestimating the training. Users need 30 minutes, not 30 seconds. Do it twice: once the week before and once the week after.
Forgetting to redirect the 0800. Every migration we have seen, someone forgets a number.
Leaving the old PBX in place “just in case”. You will never turn it off, and you will carry the line rental forever. Decommission it properly.
What we would do
For a typical 40-person SMB on Microsoft 365 today, we would move to Teams Phone with direct routing via Gamma. Port numbers with two weeks notice, replace the handsets, enrol the softphones, train the users, retire the old PBX within 30 days. Budget £120 to £180 per seat for handsets, £6 to £10 per user per month for the service.
Our connectivity team handles PSTN migrations every week. If yours is outstanding, let us run the plan.