The PSTN switch off explained: what happens to the public switched telephone network
The PSTN switch off is the closure of the UK’s copper telephone network on 31 January 2027. PSTN stands for public switched telephone network, the circuit-switched copper infrastructure that has carried British landline calls since the nineteenth century. When it closes, analogue lines and ISDN stop working, along with ADSL and FTTC broadband and a surprising amount of equipment that dials out over a phone line without anyone thinking of it as a phone.
The date has moved once already, from December 2025, which has bred reasonable scepticism about whether it will move again. Openreach says it won’t, and the reasoning holds up better than most deadline talk: the extension was granted specifically to solve telecare migration, that work completed in October 2025, and the wholesale price rises staged through 2026 were built to make delay costly.
At the six-months-to-go mark this summer, Openreach counted roughly 1.5 million lines still on copper. Around 350,000 sit at business premises, all drawing on the same engineers and installation slots between now and January.
What follows covers the network itself, which dates constrain you, and what breaks. The mechanics of migrating are handled separately in our landline-to-VoIP guide.
Table of Contents
What the public switched telephone network is
Dial a number on a traditional landline and the handset converts your speech into an analogue electrical signal. That signal travels down a copper pair to your local exchange. The exchange routes it through trunk switches to the destination exchange, and a dedicated circuit stays open for the entire call, silences included. Hang up and the circuit is released.
This is circuit switching, and it is why the network is described as “switched”. Every call reserves a physical path for its own exclusive use.
The design is a genuine engineering achievement and hopelessly inefficient by current standards. An IP network breaks voice into packets, sends them across shared capacity alongside everything else, and reassembles them at the far end. It uses bandwidth only when there is something to carry.
What PSTN covers, and what it doesn’t
PSTN is often used loosely to mean “old phone stuff”. Precisely, it covers analogue voice lines and the exchange infrastructure behind them. ISDN2 and ISDN30 are separate products built on top of that same infrastructure, which is why they close on the same date. ADSL and FTTC broadband ride the same copper pairs and go with them.
Full fibre, SOGEA and mobile are unaffected. If your broadband already arrives over fibre to the premises and your calls already run through an app or a SIP trunk, the switch off is largely somebody else’s problem.
Why Openreach is retiring it
Two national networks cost more to run than one of them earns. The copper estate is old, maintenance gets harder each year as spares and specialist skills thin out, and full fibre coverage has reached the point where parallel operation makes no financial sense.
Worth being clear on one thing: this is a wholesale withdrawal, not a commercial decision by a single retailer. Openreach is removing the product that nearly every UK provider resells. BT, Sky, TalkTalk, Vodafone and the others all sit downstream of the same closure, so changing supplier changes nothing about your deadline.
Openreach has branded the final phase of this the Big Switch Off, which is the term you will now see in most industry coverage.
The dates that actually constrain you
31 January 2027 is the national date. For most businesses it isn’t the operative one.
Stop-sell
Before an exchange area is switched off it enters stop-sell. From that point you cannot order new copper services or modify existing ones. No new lines, no extra channels, no package changes. Stop-sell has been rolling since 2023 and now covers most of the country.
The test is simple. Ring your provider to add a line, and if the answer is no, your migration window has already opened whatever the national date says. A sales team hiring into a stop-sell exchange hits this well before January: three new starters, no way to give them lines.
The price staircase
Openreach has used wholesale pricing to force movement. Against the £10.65 (ex VAT) baseline for basic Wholesale Line Rental:
- 01/04/2026 — up 20%, to roughly £12.78
- 01/07/2026 — up a further 40% of the baseline
- 01/10/2026 — another 40%, roughly doubling the 2025 rate
Two of the three have landed. Whether your provider has passed them through is worth establishing before the October step, because for many organisations an all-IP line already costs less than the copper one it would replace.
What stops working
Phones are the obvious casualty and rarely the expensive one. Anything that dials out over a copper pair is in scope:
- Lift emergency lines and disabled refuge intercoms
- Monitored intruder and fire alarm signalling
- Card payment and PDQ terminals
- Door entry and access control systems
- Fax lines, franking machines, older building management kit
- ADSL and FTTC broadband
Lift alarms are the ones that keep facilities managers awake. A lift emergency phone going dead is a safety and compliance failure rather than an inconvenience, and the line is very often on a separate account IT has never seen. Sites that have changed hands, or where facilities and IT report into different budgets, hold the most orphaned lines.
Card terminals fail more quietly. A PDQ machine on an analogue line stops authorising, and the discovery usually arrives as a queue of customers rather than a monitoring alert.
The ISDN switch off
ISDN2 and ISDN30 are withdrawn on 31 January 2027 alongside the PSTN, because ISDN was layered on the same exchange infrastructure. When the network below closes, the services above close with it.
An on-premise PBX fed by ISDN30 channels is a harder migration than a couple of analogue lines, mostly because of numbers. A single geographic number ports in ten to fourteen working days. A DDI range takes considerably longer, and the timeline depends partly on a losing provider with no commercial incentive to hurry. Contact centres and outbound sales floors should lodge those ports early and plan a parallel-running period rather than a cutover weekend.
SIP trunking keeps an existing PBX alive over IP and is usually the least disruptive route. Whether the PBX is still worth keeping is a separate question, generally answered differently once the hardware refresh quote lands.
PSTN replacement options
The right one depends less on the phones than on what else is on the line.
Digital voice over SOGEA or full fibre. The closest like-for-like swap. The line becomes broadband-only, voice runs over it, and your existing handsets can often stay. Fine for a single-site business with a handful of lines and no ambition beyond making and taking calls. It replaces the line, not the phone system, so if your setup is already frustrating, it stays frustrating.
A SIP trunk is the digital equivalent of the copper pipe: it carries calls over the internet into the on-premise phone system, the PBX (Private Branch Exchange), you already own. Entirely legitimate and Ofcom-regulated, despite the reputation SIP picked up from unrelated fraud.
It makes sense in one specific case: a recent, well-specified PBX plus a large estate of direct-dial numbers you’d rather not re-point. You keep the hardware, which means you keep maintaining it, refreshing it, and paying someone who understands it.
A cloud phone system. No PBX, no trunk, nothing on site. Numbers live in the platform, calls route to whichever device the person is actually using, and the system updates itself. This is the option that changes what your team can do rather than just keeping the lights on: calls logged to the CRM automatically, recordings and transcripts available to whoever coaches the team, a new starter live in minutes instead of an engineer visit.
Everything that isn’t a phone needs its own plan. Alarm signalling moves to a dedicated IP or mobile path, card terminals to broadband or 4G, lift lines to a GSM dialler. These are separate procurement conversations, and they’re the ones most likely to be forgotten until they fail. Openreach estimates 1.5 million lines are still on legacy copper, including roughly 350,000 business premises, a large share of those are devices nobody has thought about in years.
Are landlines being phased out in the UK?
No, although the way this gets reported invites that reading. Landline calling continues. The transmission underneath it changes from copper to internet protocol.
Your geographic number survives, customers dial the same digits and hear the same ring. This is already how BT Digital Voice, Sky Voice and every business VoIP platform work.
Porting is protected under Ofcom’s rules: your outgoing provider cannot charge you to move a number away, though early termination charges on the contract itself may still apply. Porting is also the only part of a migration not fully within your control, since it needs cooperation from the provider you’re leaving. Lodge it earlier than seems necessary.
Who gets protected
The 2025-to-2027 extension was granted largely for telecare users, an estimated 1.8 million people relying on pendant alarms and health monitors that weren’t reliably compatible with digital lines. Openreach’s Prove Telecare service, live nationwide since October 2025, exists to migrate them safely, and its completion is why the industry now treats the deadline as fixed.
Providers also carry Ofcom obligations around power cuts. Copper lines drew power from the exchange and IP lines don’t, so at-risk customers must be offered a way to reach 999 during an outage, usually a battery back-up unit.
None of this extends to businesses. There is no protective migration scheme for a company, no grace period, and no mechanism that flags you as unmigrated. After the switch-off date, remaining PSTN services fall back to limited emergency access, a public safety measure that will not carry your customer calls.
How this goes wrong in practice
Almost nobody misses the deadline through ignorance of it. They miss it by writing “sort out phones” in the January 2027 diary without having counted their lines, then finding in week one that the count was wrong.
For a solo consultant or trades business, the exposure sits in a single number printed on the website, the invoices, the van and a Google Business Profile carrying years of local search history. Porting keeps it. Leaving the port until December 2026 puts the one asset that generates enquiries into a queue.
Sales teams face a scheduling problem more than a technical one. A DDI (Direct Dial-In) range ports slowly, and a phone system that is also the pipeline can’t be cut over on a Friday and debugged on Monday. The pilot group and the overlap week exist to catch the routing rule nobody tested.
RevOps has the most to gain, because the migration is a rare chance to fix data capture rather than reproduce it. Copper generates no usable call data at all: no automatic logging, no attribution, no record of what was said. If the whole voice estate is being rebuilt regardless, specifying that calls land in HubSpot, Pipedrive or Salesforce without anyone retyping them costs nothing at the point of purchase and is tedious to retrofit later. Rebuilding on a cloud platform that carries copper’s blind spots across is a lot of work for no analytical return.
Onoff Business covers the version of this involving no handsets and no engineer visit. Each person gets a business number in an app on the phone they already carry, existing numbers move across by porting, and calls, SMS and voicemail sync into the CRM automatically. For distributed teams, or sales floors that stopped sitting at fixed desks years ago, that usually fits better than recreating a desk-phone estate in software.
Switch to VoIP without disrupting your business
Get ahead of the PSTN switch-off with Onoff Business. Port your existing numbers so nothing changes for your customers, and run calls, SMS and voicemail from one cloud phone system that syncs straight into your CRM.
Not sure where to start? Read our complete guide to switching from a landline to VoIP in the UK.
Public switched telephone network. It is the analogue, circuit-switched copper infrastructure connecting traditional landline phones to local exchanges, in use across the UK since the nineteenth century.
A standard analogue phone line running over a copper pair to your local exchange. If your phone plugs into a socket in the wall and the service isn’t described as digital voice, VoIP or fibre, it is almost certainly a PSTN line.
Your handset converts speech into an analogue electrical signal that travels along copper to the exchange, which routes it through trunk switches to the destination. A dedicated circuit is held open for the whole call and released when you hang up.
The withdrawal of ISDN2 and ISDN30 services on 31 January 2027, the same date as the PSTN closure. ISDN was built on the same exchange infrastructure, so it cannot outlive the network beneath it. Businesses running a PBX over ISDN30 need to allow extra time to port a DDI range.
31 January 2027 nationally. Most businesses hit an earlier constraint when their exchange area enters stop-sell, which blocks new copper orders and changes to existing lines, and stop-sell already covers most of the UK.
Analogue and ISDN lines stop working, and anything depending on them, including alarms, lift lines and card terminals, loses service until moved to a digital alternative. Businesses sit outside the protective arrangements covering telecare users and get no commercial grace period.
Less than the deadline implies, if you go cloud: no engineer visit, no hardware to specify, just users and numbers. The slow part is porting your existing numbers, which runs on your outgoing provider’s clock: start early, that queue lengthens as January 2027 approaches. The question worth asking while you’re forced to look at this anyway is whether the replacement gives you anything back, or just keeps your reps copy-pasting call notes into the CRM. That gap is what Onoff Business was built for, so take that as a disclosure rather than a neutral recommendation.