Can You Keep Your Business Landline Number When You Switch?

Quick answer

Yes - you keep your number. Number portability is a regulated right in the UK, and it applies to geographic numbers, non-geographic numbers and full DDI ranges alike. The line is being switched off; the number is not. Your new provider submits the port, you agree a date, and on that date calls to your existing number start arriving on the new service. Customers notice nothing.

The risks are practical rather than existential. Ports get rejected over mismatched account details, they take longer than people allow for, and every so often a business loses a number permanently by cancelling the old line first. That last one is the only genuinely unrecoverable mistake in the whole switch-off, which is why it gets its own section below. If you would rather hand the whole thing over, get a no-obligation quote and we will run the port for you.

Why the number survives when the line does not

It helps to see them as two separate things that used to arrive together. The line was a physical copper pair rented from Openreach. The number is an entry in the national numbering system, allocated by Ofcom to a communications provider and assigned by them to you.

When the copper goes, the line ends. The numbering entry does not - it just needs to point at a different provider and a different service. That redirection is what porting is, and the mechanics are the same well-trodden process used every time a business changes provider, described in general terms in our guide to number porting. This page covers the landline-specific version: what you can keep, what can go wrong, and the sequencing around a switch-off migration.

What you can keep, and the rare cases you cannot

The final two rows are worth ten minutes of checking. If you bought your phone service through a reseller, ask specifically who the range holder is and confirm in writing that the numbers port with you. Our phone number checker will tell you which provider currently holds the range your number sits in, which is a useful sanity check before you start.

How a port actually runs

Two to four weeks is a fair planning assumption for a straightforward geographic number. A large DDI range, a disputed account or a reseller in the chain can push it out further. Since everything else in a switch-off migration has to fit around the port date, this is the item to start early - our switch-off deadline guide sets the wider timeline.

Why ports get rejected

Almost every rejection is administrative rather than technical, and almost all of them are avoidable. Before you submit, get these to match the losing provider's records exactly, not your letterhead:

• The account name, including any trading-as or limited-company suffix.
• The installation address, in the format the old bill prints it.
• The account number from a recent bill, not from an old one.
• The full list of numbers, including every DDI in the range.
• Confirmation that the account is not in arrears or subject to a dispute.
• The name of the person authorised to request the port.

The most common single cause we see is a business that changed name or legal entity years ago and never updated the telecoms account. The port is submitted for the current company, the losing provider's records show the old one, and it bounces. Fixing it means updating the account first, which adds a fortnight - so check it now rather than at the point of submission.

The one rule: port first, cease second

Everything else on this page is administration. This is the part that actually loses numbers.

If you cancel the old line before the port has completed, the number goes back to the outgoing provider's pool. At that point it is no longer yours, and recovering it depends entirely on whether it has been quarantined or reallocated and on the goodwill of a company you have just left. Sometimes it comes back. Sometimes it does not, and there is no regulator, escalation or amount of money that fixes it.

The failure mode is usually well-intentioned. A business gets its shiny new service working, notices it is paying for two things at once, and cancels the old line to stop the waste - a fortnight before the port date. The overlap they were trying to save is a few weeks of legacy rental. The number is on the van, the website, thirty years of paperwork and every customer's phone.

So: the old line stays live until the number is proven on the new service. No exceptions, no matter what the rental costs. Legacy rental has risen through 2026 and it is still cheap next to this.

Port day: what to test

Cutover usually takes minutes inside an agreed window, and the temptation is to make one call and declare victory. Test properly instead:

From outside your own network. Ring the number from a mobile on a different network. Calls from inside the building can succeed for reasons that have nothing to do with the port.

Every published number. Not just the main one. Every DDI printed on paperwork, every departmental number, the fax number if you still list one.

Both directions. Call out as well as in, and check which number the recipient sees - outbound presentation is a separate setting that frequently arrives wrong.

The routing behind the number. Hunt groups, out-of-hours diverts and voicemail have to be rebuilt on the new system; the port moves numbers, not call flows.

If you are also moving premises

A geographic number is associated with an area code rather than an exact address, so moving within the same area is straightforward, and internet-based services make keeping an out-of-area number practical too. There is more to an office move than the port, though - connectivity lead times at the new site are usually the critical path - so see moving office: phone lines and numbers for the sequencing.

If your provider tells you that you cannot keep it

Push back. Portability is a regulated obligation, and "we cannot port that" almost always means one of three more specific things: the account details do not match, there is an outstanding balance, or the number is held by a party further up the chain than the person you are speaking to. All three are solvable. Ask which of them it is, in writing, and escalate if the answer stays vague.

The bottom line

Your number is the asset; the line was only ever the delivery mechanism. It ports to whatever you move to, the process is routine, and your new provider does the work. Give it two to four weeks, make the account details match before you submit, ask for DDI ranges as whole blocks, and test from outside on the day. Then - and only then - cease the old line.

Want the port handled properly, including the awkward ranges and the numbers nobody can account for? Get a no-obligation quote or call 0333 006 9399, and we will audit your numbers before we move any of them.

Getting unknown calls on a business line? Our free UK phone number checker shows which network or provider Ofcom allocated any number to, and whether the range is in service — no sign-up.