How to switch from landline to VoIP: a 7-step guide for UK businesses
Key Takeaways
- The UK’s PSTN closes on 31 January 2027. Landlines and ISDN lines stop working.
- Stop-sell is already live in most areas, so your real deadline is likely sooner.
- 1.5 million lines are still on copper, 350,000 of them at business premises.
- You keep your numbers. Porting takes 10–14 working days and your provider can’t charge for it.
- Alarms, lifts, card terminals and fax lines go down too, not just phones.
- Businesses get no protection scheme. The safety nets cover telecare users only.
- Migrate in seven steps: inventory, port, vet the provider, pilot, run parallel, connect the CRM, decommission.
Table of Contents
Most businesses that put off switching from landline to VoIP aren’t doing it because they think their current phone lines are great. They’re doing it because the migration itself sounds risky: dropped calls during the switch, lost numbers, a week of confused clients wondering why nobody’s picking up.
Done properly, none of that has to happen. A landline-to-VoIP transition is one of the more low-risk technical changes a small business will make this year, as long as it’s sequenced correctly. This guide walks through exactly that sequence.
There’s also a deadline attached to this one. The UK’s Public Switched Telephone Network (PSTN) closes on 31 January 2027, the date Openreach retires the copper phone network that traditional landlines and ISDN lines run on. Businesses that wait until the last few months tend to get the worst of both worlds: rushed installations and no room to fix anything that goes wrong.
Why this isn’t optional anymore
PSTN and ISDN lines are being retired nationally. This isn’t one provider’s commercial decision but Openreach withdrawing the underlying copper phone service, which affects customers of every UK provider that sells on top of it.
The original deadline was December 2025. BT and Openreach pushed it to 31 January 2027 in May 2024, giving communications providers an extra 13 months to migrate customers safely, largely because of concerns about vulnerable users on telecare devices. Openreach has since said it doesn’t expect a further extension.
The more useful number is how much is still outstanding. At the six-months-to-go mark, Openreach estimated around 1.5 million lines still running on copper, roughly 350,000 of them at business premises. Those are the businesses competing for the same engineers and the same installation slots in the final quarter.
Waiting also costs money before it costs service. Openreach has confirmed tiered price increases on legacy Wholesale Line Rental products, so the longer a copper line stays active, the more it bills.
There’s a second deadline most businesses miss entirely. Before any line is physically switched off, its exchange area goes into stop-sell: you can no longer order new copper services or modify the ones you have. Stop-sell is already in force across most of the country. If you can’t add a line or change a package today, your migration window has already started, whatever the national date says.
None of this requires panic. It requires a plan, ideally one that starts months before the deadline rather than weeks.
Step 1: Map what you actually have
Before touching anything, get a real inventory. How many lines are active. Which ones are genuinely used rather than just paid for out of habit. Which numbers are printed on invoices, websites and vehicle signage. And which devices depend on a phone line to function: alarm systems, lift lines, card payment terminals, door entry systems and fax lines are the common surprises here.
This step gets skipped more than any other, usually because “we’ll figure it out as we go” feels faster. It isn’t. Migrations that go badly almost always trace back to a line or a dependency nobody remembered until it stopped working.
Step 2: Confirm your numbers can be ported
A business’s phone number is often more valuable than the line it currently runs on, especially if it’s been in use for years and is attached to reviews, ads or word of mouth. Number porting lets you keep that number and move it to a VoIP phone system, so nothing about how clients reach you has to change.
Ask any provider directly whether porting is included and how long it takes. A single geographic business number typically takes 10 to 14 working days. Multi-line setups and DDI ranges take longer, sometimes considerably.
Two things worth knowing before you start. Ofcom’s rules prohibit your existing provider from charging you to port a number out. There may be early termination charges on the contract itself, but the port is free. And this is the one step in the entire migration that isn’t fully in your control, since it depends on cooperation from the outgoing provider. Start it early.
Step 3: Check whether your provider runs the network
This is the step most guides skip, and it’s the one that matters most when something goes wrong.
Not every VoIP provider operates the network your calls run on. Many are resellers, selling access to infrastructure and number ranges owned by someone else. That’s not automatically a problem, but it does mean that when there’s an outage or a compliance question, you’re dealing with a middleman rather than the party actually responsible for the service.
One thing to get straight first: the UK doesn’t issue telecoms licences. Individual licences were replaced in 2003 by a general authorisation regime, and providers now operate under Ofcom‘s General Conditions of Entitlement rather than holding a licence you can ask to see. So “are you licensed?” isn’t the useful question.
The useful question is whether they hold their own number ranges and run their own network, or resell someone else’s. A provider with its own numbering allocation is directly accountable for porting, routing and emergency call compliance. A reseller has to escalate to whoever actually is. Ask it plainly. The answer tells you who picks up the phone when there’s a problem.
Step 4: Pilot with a small group first
Don’t migrate the whole company on day one. Pick a small group, ideally one that’s vocal about problems rather than quietly working around them, and run the new system alongside the old one for a week or two.
This surfaces the issues that never show up in a demo: a call quality problem on one specific office Wi-Fi network, a routing rule that doesn’t match how the team actually answers calls, a workflow that assumed a physical desk phone that no longer exists. It’s far easier to fix these when they affect three people than when they affect thirty.
Step 5: Run both systems in parallel
The riskiest way to migrate is cutting the old system off the same day the new one goes live. If anything is wrong (misconfigured routing, a number that didn’t port cleanly, a team member who missed the memo) there’s no fallback.
A short overlap period of a few days to a week removes almost all of that risk. Keep the old lines active but stop relying on them, and only decommission them once the new business VoIP setup has handled a real, uneventful week of calls.
Step 6: Connect it to the tools your team already uses
A landline replacement that doesn’t talk to the CRM is a downgrade wearing a VoIP badge. If calls, whether inbound or outbound, aren’t logging automatically to whatever your sales or support team already works in, HubSpot, Pipedrive, Zoho, or similar, someone ends up manually re-entering data that should have synced on its own, or worse, it just doesn’t get logged at all.
Check this before signing anything, not after. Ask specifically how call logging, call recordings if needed, and contact syncing work with your existing CRM. This is usually the difference between a migration that actually improves reporting and one that just moves the same blind spots onto new infrastructure.
Step 7: Decommission the old lines properly
Once the new VoIP phone system has run cleanly for a full billing cycle, cancel the old lines formally. Don’t just stop paying and assume it lapses. Confirm the cancellation in writing and hold onto that confirmation, because providers occasionally keep billing lines that were cancelled verbally but never processed on paper.
This is also the moment to update every number reference still pointing at the old system. Business cards left in a drawer don’t matter. Your Google Business Profile, website footer, email signatures and any hardware still wired to the old line absolutely do.
Switch to VoIP without disrupting your business
Get ahead of the PSTN switch off with Onoff Business. Keep your existing business numbers through number porting, and bring calls, SMS and voicemail into one cloud phone system that syncs with your CRM.
Yes, in almost all cases. This is called number porting, and reputable VoIP providers handle it as a standard part of onboarding. The number moves, but the underlying technology changes from copper to internet-based calling, so nothing about how clients dial you needs to change.
Modern business VoIP, running on a stable internet connection, is generally as reliable as traditional landlines, and more flexible, since calls aren’t tied to a single physical location or device. The main variable is internet quality, a weak or overloaded connection will affect call quality more than it ever affected a copper line.
Voice over Internet Protocol. It means calls are transmitted as data over the internet rather than through traditional copper telephone lines, which is also why VoIP phone systems can run on a mobile app instead of requiring a dedicated physical phone line.
A VoIP phone system converts voice into digital data and sends it over an internet connection, either through a broadband router, a dedicated app, or both. This is why VoIP phone systems can run on a mobile, a laptop, or a desk phone interchangeably, the number belongs to the account, not to a specific piece of hardware.
Landlines aren’t disappearing, but the technology behind them is. The copper-based PSTN closes on 31 January 2027, after which landline calls run over an internet connection instead. Your number stays the same. Many businesses lose the ability to order or modify copper lines well before that date, because their exchange area has already entered stop-sell.
Yes. Each person gets a business number in an app on the phone they already carry, and your existing numbers move across through porting. Calls follow the person rather than the desk and log automatically into your CRM. No handsets, no SIM cards, no PBX, no engineer visit.