What Is PSTN? The 2027 Switch-Off Explained

By Charlie Fisher · Head of Mobile Connection · Reviewed by Andy Pickett

Published 12 March 2026 · Updated 23 September 2026 · About the author

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 on 31 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.

How many phone lines does your business need?

Get a free no-obligation quote in 60 seconds

1-2

3-9

10-49

50+

No obligationTakes 60 seconds

When does your current contract expire?

Out of contract

< 3 months

3 months+

Not sure

← Back

Tell us about your business

Business name *

Postcode *

Continue →← Back

Your details

First name *

Last name *

Business email *

Contact number *

Get My Free Quote →← Back

We'll never share your details. Unsubscribe anytime.

Thank you!

One of our mobile experts will be in touch shortly with your tailored quote.

TRUSTED BY

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:

1. Your telephone converts your voice into an analogue electrical signal.
2. That signal travels along a copper pair from your premises to the nearest local exchange.
3. The exchange routes the call through one or more trunk switches until it reaches the destination exchange.
4. A dedicated circuit is held open for the entire call, regardless of whether anyone is speaking.
5. 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. For most organisations, the landline voip transition is the most practical path forward.

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.

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 provider migrates you or the 31 January 2027 deadline arrives — whichever comes first.

Where Things Stand: September 2026

With just over four months to go, this is the position Openreach set out when it launched its “Big Switch Off” campaign on 27 July 2026:

• The date is fixed. The PSTN is retired on 31 January 2027. Openreach’s Director of All-IP, James Lilley, said plainly: “there is no extension to the deadline.”
• Around 1.5 million lines were still on the old network in July 2026 (down from 1.9 million in June), including roughly 350,000 business premises. Openreach has started issuing formal notifications to providers with outstanding migrations.
• Consumers get a safety net; businesses do not. Openreach is piloting Emergency Voice Access (EVAc) — a temporary, voice-only fallback for single residential lines that miss the deadline — in the Salisbury and Mildenhall exchange areas from 3 August 2026. It does not carry broadband, ISDN or alarm and lift signalling, and it is not offered on business lines. A business line that is still analogue on 1 February 2027 simply stops.
• Copper “stop sell” keeps widening. By 20 August 2026 stop sell was active in 1,572 exchanges covering around 15.4 million premises, and a further 112 exchanges (554,918 premises) were named in July. Stop sell restricts what can be ordered; it does not disconnect anyone — the national switch-off does that.
• Legacy lines are getting dearer. Openreach has been raising wholesale rental on remaining WLR lines each year, with a further increase due in October 2026, so every quarter spent on analogue costs more than the last.

The practical message for a business that has not moved yet: order the replacement service now. Number porting, broadband upgrades and engineer visits all have lead times, and those lead times lengthen as January approaches. Our PSTN switch-off business checklist walks through the audit step by step.

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 31 January 2027 switch-off:

1. Audit your lines — list every PSTN and ISDN line across all sites, including lines used by alarms, lifts, PDQ machines and fax.
2. Check your broadband — VoIP requires a stable internet connection. Confirm your broadband speed and reliability. Consider upgrading to FTTP or SoGEA if needed.
3. 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.
4. Port your numbers — you can keep your existing phone numbers when moving to VoIP. Your new provider will handle the porting process.
5. Upgrade connected devices — replace or upgrade alarms, PDQ machines, fax lines and any other equipment that depends on analogue connectivity.
6. 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.
7. 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. For businesses that have already started the landline voip transition, our guide to cloud phone systems in 2026 covers the leading platforms and pricing in detail.

Your 90-Day PSTN Switch-Off Plan

Ninety days is enough to move a 20–100 user business off analogue and ISDN lines properly — with a pilot, batch number porting and every alarm, lift phone and card terminal accounted for — but only if the long-lead items are ordered in the first fortnight. Openreach’s July 2026 count put roughly 350,000 business premises still on the old network, and every one of them is competing for the same porting slots and engineers between now and January. Work through the plan below in order; each block assumes the previous one is done.

Weeks 1–2: Audit and order the long-lead items

• List every phone line, DDI and analogue-connected device across every site — intruder and fire alarms, lift emergency phones, PDQ terminals on fallback lines, door entry, franking machines and fax. Use the services-affected list above as the checklist.
• Check broadband at each site. If you are still on FTTC or a copper line, order the FTTP or SoGEA upgrade now — install lead times are the longest part of the whole job and they lengthen as January approaches.
• Map how staff actually use the phone (desk, mobile, hybrid, hunt groups, call queues) so you buy the right licences and handsets rather than a like-for-like copy of the old system.
• Pull the contract end dates and notice periods for every existing line so nothing auto-renews or bills twice.

Weeks 3–4: Select and pilot

• Shortlist two providers and get demos, not just quotes. Confirm in writing what is included (call recording, IVR, mobile app, UK support) and what costs extra.
• Run a two-week pilot with one team or one site alongside the old lines. Test inbound, outbound, transfers, voicemail-to-email and the mobile app on real calls.
• Confirm the number porting process and timescales in writing and submit port requests as early as the provider allows — do not wait for the pilot to finish.
• Order replacement kit for the analogue devices you found in the audit (IP or 4G alarm communicators, IP lift phones, 4G/IP card terminals). These need their own supplier lead times.

Weeks 5–10: Roll out

• Port numbers in batches — site by site or department by department — and never in the last week before Christmas.
• Deploy handsets and softphone apps with a written cutover plan for each site: who moves when, who tests, who signs off.
• Train staff. Even simple things — transferring a call, setting an out-of-hours divert — work differently on a hosted system, and untrained users are where most “VoIP problems” come from.
• Swap the analogue-dependent devices as their replacements arrive and test each one end to end (an alarm that “works” but no longer reaches the monitoring centre is the classic miss).

Weeks 11–13: Decommission and optimise

• Cease the old PSTN and ISDN lines and check the final bills — a surprising number of businesses pay for both systems for months.
• Replace anything still analogue. Business lines get no fallback: Openreach’s Emergency Voice Access pilot is for single residential lines only.
• Review call analytics after the first month and tune IVR menus, ring groups and opening hours on real data.

Done this way you cross 31 January 2027 with no drama and a phone system that is genuinely better than the one you had. Leave it until January and you will be taking whatever porting slots, engineers and handsets are left.

Hidden Risks of Leaving It to the Final Weeks

Telephony rarely feels urgent until it breaks, but several quiet risks compound the longer the migration slips.

Porting queues lengthen

Number porting is already slower than it should be. As the deadline approaches every provider submits port requests at once, so a port that took ten working days in early 2026 can take several weeks by the autumn. Submit ports early and in batches.

Engineer and handset shortages

Installers get booked out and popular handsets — Yealink, Poly, Grandstream — go on back-order. If you need 40 phones across three sites in December you may end up with whatever is in stock rather than what you chose. Our VoIP handsets and headsets buyer’s guide covers the options.

Forced migrations

If you have not moved voluntarily your provider will eventually move you — on their timeline, to their chosen product, with minimum configuration. It rarely produces the best outcome, and it is not guaranteed to happen before the line stops.

Ancillary devices get forgotten

Lift phones, alarm signalling, card terminals on fallback lines, door entry systems and franking machines each need a specific fix, and auditing them takes time you will not have in January. Consumers get a voice-only safety net in the EVAc pilot; business lines do not.

Frequently Asked Questions

When is the PSTN switch-off happening?

The national PSTN switch-off date is 31 January 2027, and in July 2026 Openreach confirmed there will be no extension. Providers are migrating customers ahead of the date, so your lines could be moved — or given a forced migration date — 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?

Business analogue and ISDN lines simply stop working on 31 January 2027. You lose the ability to make and receive calls, and any connected equipment — alarms, lift phones, PDQ machines, fax — fails with them. Only residential single lines get a temporary voice-only fallback (Emergency Voice Access); it is not offered to businesses and carries no broadband, ISDN or alarm signalling. Migrating now avoids last-minute disruption and the queue for porting and engineers that builds through the final weeks.

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.

See also our guide on SIP Trunking Explained: What It Is, How It Works & UK Costs for more details.

See also our guide on What is SIP? UK Business Guide 2026 — The Protocol Behind VoIP, Explained in Plain English for more details.

What is the PSTN switch-off and how will it affect my business phone system?

The PSTN (Public Switched Telephone Network) is the traditional copper-wire telephone network that has served the UK for over a century. BT Openreach is switching off the PSTN by January 2027, meaning all traditional analogue and ISDN phone lines will stop working.

What this means for your business:

• Traditional landlines and ISDN lines will no longer function after the switch-off date
• Any equipment connected to analogue lines (fax machines, alarm systems, door entry systems, PDQ machines) will need to be migrated
• Openreach has already stopped selling new ISDN lines and is actively migrating exchanges

What you need to do:

• Audit your current setup – identify all services that rely on traditional phone lines
• Switch to VoIP – a hosted VoIP phone system runs over your broadband and is the direct replacement for PSTN and ISDN services
• Upgrade your broadband – ensure you have a reliable internet connection capable of handling voice traffic
• Port your numbers – your existing business phone numbers can be transferred to your new VoIP system
• Plan early – do not wait until the last minute as demand for migration services will increase as the deadline approaches

Connection Technologies is helping hundreds of UK businesses prepare for the PSTN switch-off. Get a free migration assessment to ensure your business is ready.

What features come with a business VoIP system?

Business VoIP includes call routing, voicemail-to-email, auto-attendant, call recording, CRM integration, mobile apps and detailed analytics. Connection Technologies configures all features as part of the setup.

See also our guide on Leased Line vs FTTP for Business UK: Speed, Cost & Reliability for more details.

Start Your Migration Today

The PSTN switch-off is not a distant event — exchanges are already being migrated and the final deadline is only weeks 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.

Written by

Charlie Fisher

Head of Mobile Connection

Charlie is the Head of Mobile Connections at Connection Technologies, responsible for leading the mobile division and ensuring the delivery of high-quality, reliable solutions to businesses across the UK.

Business MobilesMobile StrategyNetwork Solutions

View Full Profile