The Public Switched Telephone Network — better known as PSTN — has been the backbone of UK telephony for well over a century. Every traditional landline call, fax transmission and dial-up connection has travelled across this copper-wire network. But Openreach has confirmed that the entire PSTN will be permanently switched off by January 2027, and every business that still relies on analogue or ISDN lines needs a migration plan.
This guide explains exactly what PSTN is, how it works, why the 2027 switch-off is happening, the key Openreach milestones, what replaces it and the practical steps UK businesses should take now. If you already know you need to move and just want pricing, get a free business phone quote or call us on 0333 015 2615.
What Is PSTN?
PSTN stands for Public Switched Telephone Network. It is the traditional circuit-switched telephone system that connects callers through a network of copper wires, local exchanges, trunk lines and switching centres. When you pick up a traditional landline handset and hear a dial tone, you are connected to the PSTN.
The network dates back to the late 19th century. Over the decades it evolved from manual operator switchboards to automated electronic exchanges, but the fundamental principle remained the same: a dedicated copper circuit is established between two endpoints for the duration of each call.
How PSTN Works
When you dial a number on a traditional landline, the following happens:
- Your telephone converts your voice into an analogue electrical signal.
- That signal travels along a copper pair from your premises to the nearest local exchange.
- The exchange routes the call through one or more trunk switches until it reaches the destination exchange.
- A dedicated circuit is held open for the entire call, regardless of whether anyone is speaking.
- When you hang up, the circuit is released.
This circuit-switched approach is reliable but extremely inefficient by modern standards. A dedicated line is reserved even during silences, and the copper infrastructure requires constant physical maintenance.
What Is ISDN and How Does It Relate to PSTN?
ISDN (Integrated Services Digital Network) is a digital upgrade that sits on top of the PSTN copper infrastructure. It was introduced in the 1980s to offer faster data transfer and the ability to carry voice and data simultaneously. Many UK businesses use ISDN2e (two channels) or ISDN30 (up to 30 channels) for their phone systems.
Because ISDN relies on the same underlying copper network, the ISDN switch-off is happening at the same time as the PSTN switch-off. Both technologies will cease to function when Openreach retires the copper exchanges.
Why Is PSTN Being Switched Off?
Openreach — the infrastructure arm of BT that maintains the UK’s telephone network — has given several reasons for retiring the PSTN:
- Ageing infrastructure — much of the copper network is decades old and increasingly expensive to maintain. Spare parts for legacy exchange equipment are becoming scarce.
- Declining usage — traditional landline call volumes have fallen sharply as businesses and consumers move to mobile and internet-based calling.
- Inefficiency — circuit-switched technology wastes bandwidth. Modern packet-switched (IP) networks carry far more data over the same physical routes.
- Full-fibre rollout — Openreach is investing billions in fibre-to-the-premises (FTTP) broadband. Maintaining a parallel copper network alongside fibre is neither practical nor cost-effective.
In short, the PSTN has served the UK well, but it is no longer fit for purpose in a digital-first economy.
PSTN Switch-Off Timeline: Key Openreach Milestones
Openreach has published a phased timeline for the 2027 switch-off. The table below summarises the critical dates every UK business should know.
| Date | Milestone |
|---|---|
| September 2023 | Openreach stopped selling new PSTN and ISDN products nationwide (the “stop sell”). |
| December 2025 | Accelerated exchanges — over 100 exchanges entered “all-IP” mode with forced migration of remaining lines. |
| Throughout 2026 | Bulk migration phase — Openreach works with providers to move remaining PSTN/ISDN customers onto IP-based services. |
| January 2027 | Full PSTN and ISDN switch-off. All remaining analogue and ISDN lines cease to function. |
If your business still has traditional phone lines, the stop sell means you can no longer order new ones. Existing lines will continue to work until your exchange is migrated or the final January 2027 deadline arrives — whichever comes first.
What Replaces PSTN?
Two technologies are replacing the Public Switched Telephone Network for UK businesses:
VoIP (Voice over Internet Protocol)
VoIP routes voice calls over your broadband connection instead of a copper circuit. Calls are converted into data packets, sent across the internet and reassembled at the other end. Modern hosted VoIP platforms offer call quality that matches or exceeds traditional landlines, along with features such as auto-attendant, call recording, mobile apps and CRM integration.
For a detailed comparison of VoIP and traditional landlines, read our guide to VoIP vs landline for business.
SoGEA (Single Order Generic Ethernet Access)
SoGEA is a broadband-only line that does not carry a traditional phone service. It delivers the same speeds as FTTC broadband but without an underlying PSTN voice channel. If your business needs broadband and plans to use VoIP for calls, SoGEA is the most cost-effective connection because you are not paying for a phone line you will never use. Our SoGEA broadband guide covers how it works and who it suits.
Services Affected by the PSTN Switch-Off
The PSTN switch-off does not only affect voice calls. Many businesses have equipment and services that rely on analogue lines without realising it:
- Intruder and fire alarms — many monitored alarm systems use PSTN lines to dial the monitoring centre. These will stop working after the switch-off unless upgraded to IP or mobile-based communicators.
- PDQ/card payment machines — older chip-and-PIN terminals that dial out over a phone line will need replacing with IP or 4G-connected models.
- Fax machines — traditional fax relies on PSTN. Businesses still using fax will need to move to an online fax service or fax-over-IP solution.
- Door entry systems — intercom and access control systems that call a landline number will require IP-compatible replacements.
- Lift emergency phones — legally required emergency telephones in passenger lifts often use analogue lines and must be migrated to a compliant alternative.
- EPOS systems — some older electronic point-of-sale systems connect via PSTN for transaction processing or end-of-day uploads.
- Franking machines — postal franking machines that update tariffs over a phone line will need an IP or mobile data connection.
Auditing every device connected to your phone lines is a critical first step. Missing even one can cause a service outage after migration.
Business Migration Checklist
Use this checklist to make sure your business is ready before the 2027 switch-off:
- Audit your lines — list every PSTN and ISDN line across all sites, including lines used by alarms, lifts, PDQ machines and fax.
- Check your broadband — VoIP requires a stable internet connection. Confirm your broadband speed and reliability. Consider upgrading to FTTP or SoGEA if needed.
- Choose a VoIP provider — look for a hosted VoIP platform that includes the features your business needs: call routing, voicemail-to-email, mobile apps and number porting.
- Port your numbers — you can keep your existing phone numbers when moving to VoIP. Your new provider will handle the porting process.
- Upgrade connected devices — replace or upgrade alarms, PDQ machines, fax lines and any other equipment that depends on analogue connectivity.
- Test before you switch — run VoIP alongside your existing lines for a trial period to confirm call quality and reliability before cancelling the old service.
- Train your team — VoIP handsets and softphone apps work differently from traditional phones. Brief your staff on the new system before go-live.
Need help working through this list? Get a free business phone quote and our team will audit your current setup and recommend the right replacement at no cost.
Frequently Asked Questions
When is the PSTN switch-off happening?
Openreach will complete the full PSTN switch-off by January 2027. However, many exchanges are being migrated earlier as part of the phased rollout that began in 2023. Your lines could be affected before the final deadline.
Will I lose my phone number?
No. You can port your existing landline numbers to a VoIP service. The process is managed by your new provider and typically takes 10–15 working days. There is no need to reprint stationery or update your website.
Is VoIP reliable enough for business use?
Yes. Modern hosted VoIP platforms deliver 99.9%+ uptime and HD voice quality, provided you have a stable broadband connection. Many businesses find VoIP more reliable than ageing PSTN lines because the infrastructure is newer and actively maintained.
What happens if I do nothing before 2027?
Your analogue and ISDN lines will simply stop working when your exchange is switched off. You will lose the ability to make and receive calls, and any connected equipment — alarms, PDQ machines, fax — will also fail. Migrating proactively avoids last-minute disruption.
How much does it cost to move from PSTN to VoIP?
Hosted VoIP typically costs between £8 and £15 per user per month, which is often cheaper than maintaining traditional PSTN lines and call charges. Hardware costs depend on whether you choose desk phones, cordless handsets or softphone apps on existing devices. For a tailored quote, call us on 0333 015 2615.
Do I need fibre broadband for VoIP?
Fibre is not strictly required, but it is strongly recommended. A single VoIP call uses around 100 Kbps, so a standard FTTC connection can handle multiple simultaneous calls comfortably. If you have a large team or heavy data usage alongside voice, FTTP or a dedicated leased line will give you the headroom you need.
Start Your Migration Today
The PSTN switch-off is not a distant event — exchanges are already being migrated and the final deadline is less than a year away. Businesses that act now have the luxury of choosing the best solution at their own pace, rather than scrambling at the last minute when demand for installations peaks.
Whether you need a full hosted VoIP system, SoGEA broadband or simply advice on which of your services are affected, we can help. Get a free business phone quote or call us on 0333 015 2615 to speak with our team today.