In short
No, your number does not change when you switch to VoIP. UK numbers are portable by law, so your existing number moves to the new provider through a process called porting, which typically takes one to four weeks and switches over in minutes on the day itself.
The one real risk is cancelling the old line before the port completes. A cancelled number can be lost for good, so the old service stays live until the number has moved.
The number is usually the last thing holding a business on an old phone system. It is on the van, the signage, the invoices, ten years of Google listings, and in the phones of every customer who has ever rung. Losing it is unthinkable, so the switch keeps getting parked.
The good news is that the fear is out of date. Number porting is a regulated, routine process, and your provider does almost all of it. What follows is what actually happens, stage by stage, and the small number of things that genuinely can go wrong.
Your number is yours to move, by regulation
Ofcom requires UK providers to let customers take their numbers with them, and that applies to geographic numbers such as 0161 and 0113, non-geographic numbers such as 0330 and 0800, and whole ranges with direct dials. The losing provider is not allowed to refuse the port because you are leaving, and they are not allowed to charge you to keep your own number hostage.
What they can do is drag their feet within the rules, which is why the timescales below are ranges, not promises.
What porting actually involves, stage by stage
1. The letter of authority
You sign a letter of authority giving the new provider permission to move the number. This is the only paperwork you touch, and getting the details exactly right matters more than it looks: the company name, address and number on the letter must match what the current provider holds, or the port bounces and the clock restarts.
2. The port request and the date
The gaining provider submits the request to the losing one, who checks it and either accepts a port date or rejects it with a reason. Single numbers typically complete in one to two weeks; multi-line systems and number ranges run nearer two to four, occasionally longer where an old provider is slow.
3. Porting day
On the day, the number lifts from the old network and lands on the new one, usually inside a working hour. Calls in progress are unaffected and the new system is already configured and waiting, so most businesses notice nothing at all. We schedule ports mid-week and mid-morning, never a Friday afternoon, so any snag is fixed while everyone who can fix it is at a desk.
4. After the port
The old contract for that line ends once the number has gone, and only then. Anything else that rode on the old line, such as an alarm dialler or a card terminal, needs to have been moved beforehand, which is a survey question, not a porting one.
The one mistake that genuinely loses numbers
Cancelling the old service before the port completes. A port moves a live number; a cancelled number goes back into the old provider's pool, and recovering it ranges from slow to impossible. It is the single porting disaster worth worrying about, and it is entirely avoidable: leave the old line alone and let the port end the contract for you.
The overlap means paying for both services for a few weeks. That is the correct cost of moving a number safely, not a sign something has gone wrong, and it is a few weeks of line rental against a number the business has spent years putting on everything it owns.
What you gain once the number is on VoIP
Once ported, the number stops being tied to a wall socket. It can ring desk phones, mobiles and laptops together, follow a hunt group, play a proper out-of-hours message, and move premises with you without ever changing again. For most businesses the port is the last time the number and a physical line have anything to do with each other.
How Core Comms can help
We handle the whole port as part of every business telephone system we install: the letter of authority, the chasing, the mid-week port date, and a system configured and tested before the number ever moves. Nothing is cancelled until your number is safely across, and if the old provider drags their feet, the chasing is our job rather than yours.
If a number you cannot afford to lose is the thing keeping you on an old system, talk to our team or call 0330 838 1000 and we will walk you through the port before you commit to anything.
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