The UK's traditional telephone network, the public switched telephone network or PSTN, is being switched off. Calls are moving to digital services that run over broadband. For households the change is mostly invisible. For businesses it touches phone lines, ISDN circuits, alarms, payment terminals and lift phones, and it is a natural moment to decide how calls should be answered in future.
Timelines in this programme have moved before. Check the dates with Ofcom and your provider rather than relying on any article, including this one.
What is happening, and when
Ofcom's consumer guidance says BT plans to retire its old landline network by 31 January 2027. Openreach, which runs most of the UK's local access network, told Ofcom in December 2025 that it stopped new supply of its Wholesale Line Rental (WLR) and ISDN2 and ISDN30 products in September 2023 and will withdraw them on 31 January 2027. Ofcom notes that other networks, such as Virgin Media O2 and KCOM, had not set dates at the time of its update.
WLR is the wholesale product behind most traditional analogue business lines. ISDN2 and ISDN30 are the digital circuits that many older business phone systems still use for multiple simultaneous calls. Both are affected.
Who needs to act
- Businesses with an on-site phone system on ISDN. The circuits are being withdrawn. Businesses typically move to SIP trunks into their existing phone system, or to a hosted (cloud) phone system.
- Businesses with analogue lines. Your provider will move you to a digital service. Phones usually plug into the router instead of the wall socket.
- Anything else plugged into a phone line. Alarms, telecare devices, card terminals, franking machines, door entry and lift emergency lines may need changes or replacement. Ask the supplier of each device.
Ofcom also expects providers to offer customers who depend on their landline, for example those without mobile signal or with telecare, a free back-up solution that keeps calls to emergency services working for at least an hour in a power cut.
Keeping your number
Your phone number is usually the most valuable part of the line. Ofcom's rules on number portability let customers keep their numbers when changing provider, for both geographic and non-geographic numbers. Ofcom's switching guidance says you can still ask to keep your number for free as long as you ask within one month of cancelling, but the simplest route is to ask your new provider to port it as part of the switch, before anything is cancelled.
When you move to SIP trunks or a hosted system, ask for the numbers to be ported, check that every number, including any you only use for fax or alarms, is on the list, and agree a date and time with a fallback.
SIP trunks or hosted phone system?
| SIP trunks into your PBX | Hosted phone system | |
|---|---|---|
| What changes | ISDN circuits replaced by SIP over your internet connection | The phone system itself moves to the cloud |
| Keep your current phones | Usually, if the PBX supports SIP | Often replaced with IP phones or apps |
| Good for | Recently upgraded on-site systems | Ageing systems, multiple sites, remote staff |
| Watch out for | Router settings, firewall rules, bandwidth | Contract terms, porting all numbers |
Either way, your phones will depend on your internet connection. Our hardware checklist covers bandwidth, router settings and power.
Where an AI receptionist fits
Moving to digital calling makes it far easier to add an AI receptionist, because calls are already flowing over IP. Common patterns:
- Divert unanswered calls. Most UK landlines support call diversion. On BT lines, for example, divert-on-no-reply sends calls unanswered after 15 seconds to another number, and divert-when-busy catches calls while the line is engaged. Point the diversion at your AI number and nothing else changes. Diverted calls are usually charged to you, so check the cost to the destination number.
- AI first, team second. Calls reach the AI first, which answers routine questions and takes details, with the rest passed to staff.
- Out of hours only. A hosted phone system can route calls to the AI on a schedule.
Whichever you choose, tell callers they are speaking to an AI assistant and whether calls are recorded, and keep within the rules on caller ID and data protection. See UK rules for AI phone calls.
A switch-off checklist
- List every line and number you pay for, and what each one is used for.
- Identify every device connected to a phone line, including alarms and lifts, and contact their suppliers.
- Decide between SIP trunks and a hosted phone system.
- Check your internet connection and consider a back-up connection.
- Arrange number porting with your new provider before cancelling anything.
- Decide how calls will be answered after hours and when the team is busy, and whether an AI receptionist should take them.
- Test everything, including emergency calls, before the old service ends.
Sources and further reading
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