In January 2027, BT will switch off the UK Public Switched Telephone Network for good. ISDN30, ISDN2, traditional analogue lines — all of it. For most SMBs this is not a crisis, but it is a deadline that needs respecting, because the closer it gets, the harder it will be to get a porting slot or an engineer.
Here is the calm version of what to do, and when.
This quarter: take stock
- List every phone number, fax line, alarm line, lift line and PDQ line in the business. Yes, including the ones in the meeting rooms nobody uses.
- Identify who the lines belong to (BT, a reseller, a different carrier) and when their contracts expire.
- Note any analogue-only kit: alarm panels, lift autodiallers, door entry phones, franking machines, legacy fax. These are the most likely sources of late surprises.
This year: choose your direction
There are three sensible destinations for most SMBs:
- Teams Phone — best if your people already live in Teams and your call volumes are normal.
- A hosted cloud PBX (3CX, Gamma, 8x8, RingCentral and similar) — best if you need contact-centre features, complex IVRs, or operator-style call handling.
- A managed SIP service for an existing on-premise PBX — best if you have recently invested in a PBX you want to keep.
For each, you also need to decide what happens to the awkward analogue devices. Most can move to an ATA (analogue-to-IP adapter); some, particularly old alarm panels, need replacement.
Six months out: port and test
Number porting in the UK is no longer slow — but the system gets busier as the deadline approaches. Porting your main DDIs at least three months before contract end gives you margin to retest before the legacy lines disappear.
What you can safely defer
Decisions about which handset model, which headset, which call-recording add-on. These are real choices but they are not the urgent ones. Get the platform, the numbers and the analogue devices sorted; the rest follows easily.
The single biggest mistake
Treating the switch-off as a telephony problem. It is a connectivity problem. If the broadband at a site is not reliable enough for voice, no amount of clever PBX configuration will save the calls. Audit the lines and the routers in the same exercise.
