How to Port a Business Phone Number in the UK (and Keep It)

• Written by: Simplify Networks
• October 12, 2026

Your phone number is printed on your vans, your website, your invoices and in years of customer contacts. So when you move to a new phone system, the first worry is usually “will we lose our number?” The good news is that you almost certainly won’t. In the UK you have the right to port a business phone number to a new provider, and with a little preparation it’s a calm, mostly behind-the-scenes job.

This guide explains how porting works, what information you’ll need, how long it takes, and the handful of mistakes that cause delays or, in the worst case, a lost number.

What does it mean to port a business phone number?

Porting simply means moving a phone number from one provider to another. The number stays the same; what changes is the company that routes calls to it. Most businesses port their numbers when they move from a traditional BT-style landline or ISDN to a hosted phone system, and with the PSTN switch-off due by 31 January 2027, a lot of businesses are doing exactly that right now.

Number portability is a regulated right in the UK, set out in Ofcom’s General Conditions. In practice that means your current provider can’t refuse to release your number for general business reasons.

Which numbers can be ported?

• Geographic numbers such as 0115 (Nottingham), 0121 (Birmingham) or 020 (London). These are the most common and usually the simplest.
• Multi-line numbers and DDI ranges, where you have a main number plus a block of direct-dial numbers for staff.
• Non-geographic numbers such as 0333, 0345 and 0800. These can be ported too, but they normally take longer.

Occasionally a number can’t be ported, for example because of the way an old provider holds it. A good provider will check this before anything is switched, so you’re never left without a working number.

How to port your business number: step by step

The new provider does the heavy lifting. You don’t need to contact your old provider to start the process, and you shouldn’t cancel anything yet (more on that below).

1. Choose your new phone system. Agree how many users you need and set up the new system first. Most providers give you a temporary number so you can test everything before the port.
2. Gather your details. You’ll need a recent bill from your current provider, which shows the information the port request has to match.
3. Sign a Letter of Authority (LOA). This is a short form, signed by the account holder, that authorises the new provider to request the port on your behalf.
4. The new provider submits the request. Your current provider and the network operator validate the details and agree a port date.
5. Port day. On the agreed date your number moves across, usually during the working day. There can be a short gap of a few minutes while calls start routing to the new system.
6. Check, then cancel. Once you’ve confirmed calls are arriving on the new system, you can deal with any remaining services on the old account.

The information that must match

Most port rejections come down to small mismatches. Before you sign the LOA, check these against your latest bill:

• The exact name of your current provider
• Your account number with them
• The installation address and postcode where the line is
• The main billing number and every other number you want to bring across
• The name of the account holder

If your business has moved premises, changed its name or inherited a line from a previous owner, mention it early. Those are the cases where details most often don’t line up.

How long does number porting take in the UK?

Timescales depend on how many numbers you have and how they’re set up. As a rough guide from published UK industry lead times:

• A single-line geographic number: around 5 to 10 working days
• Multi-line numbers: around 7 to 15 working days, depending on how many lines there are
• Large or complex DDI ranges: up to around 25 working days
• Non-geographic numbers (03, 08): often 17 to 27 working days

These are minimums once a correct request has been accepted, so a rejected request resets the clock. If you have a hard deadline, such as a contract ending or an office move, start early and allow a few weeks of slack.

Five mistakes that delay a port (or lose a number)

1. Cancelling your old line too soon

This is the big one. If you cancel your old phone service before the port completes, the number can be ceased. Ofcom’s rules do give you a right to request a port of a recently ceased number (within 31 days), but it’s far simpler, and safer, to keep the old service running until the new provider confirms the port is done.

2. Forgetting what else uses the line

Before a traditional line is moved, check whether anything else depends on it: broadband, burglar or fire alarms, lift emergency phones, card machines or a fax. These may need their own plan. We cover this in more detail in Will My Alarm, Lift Phone and Card Machine Work After the Switch-Off?

3. Details that don’t match the bill

An old trading name, a postcode typo or a missing secondary number is enough for a rejection. Copy details straight from the most recent bill.

4. Leaving numbers behind

Many businesses have numbers they’ve forgotten about: an old fax line, a DDI for a former manager, or a second line that rings at the back office. List everything before you start so it can all move in one go, or be deliberately left to lapse.

5. Not testing before port day

Set up your call routing, ring groups, voicemail and out-of-hours messages on the new system using the temporary number first. Then, when the port goes through, calls land exactly where they should from the first minute.

Porting as part of a wider move to VoIP

For most small businesses, porting is one step in a bigger change: replacing an old on-site phone system or landline with a cloud system. That’s a good moment to tidy up how calls are handled, too. A hosted system lets you add an auto attendant, call queues and voicemail to email, and use your office number on your mobile with an app for Android and iOS. If you already have a phone system you’re happy with, SIP trunks can carry your ported numbers instead.

At Simplify Networks, number transfer is free: we handle the Letter of Authority, the request and the port date, and we’ll check your setup before anything is switched. Plans start from £14.99 per user per month, and our phone system migration service covers the move from start to finish. New customers who sign up by 31 October 2026 also get 50% off their first month’s per-user charges.