Porting UK numbers: how it works and what goes wrong

Porting is the single step in a phone migration that most often slips, and almost never for a technical reason. Ports get rejected because a form says Ltd where the line record says Limited. Getting the details right up front is most of the job.

What porting actually is

Your number belongs to a range allocated to a communications provider. Porting does not move the number out of that range — it leaves a permanent instruction that calls to it should be handed to a different provider instead.

That is why the losing provider has to agree, and why the number has to be live on their network at the moment the port completes. It is a redirection at the heart of the network, not a transfer of ownership.

What you need before you start

The gaining provider raises the request, but everything on it has to match the losing provider's record exactly:

• The full number list, including any that share the same installation
• The account holder name exactly as it appears on the bill, not as you would normally write it
• The installation address, including the postcode on the line record
• The account number with the losing provider
• A recent bill, usually within the last three months
• A signed letter of authority

The five rejections we see most

1. Name mismatch. The bill says one thing, the form says another. Copy the bill character for character, abbreviations and all.
2. Address mismatch. Often a unit number or a building name that was recorded differently years ago.
3. The line was already ceased. Nothing left to port from. This one is usually terminal.
4. Wrong account number. Larger providers issue several; the one on the phone bill is the one that counts.
5. The number is part of a block. Some ranges only move whole, which changes what you can request.

How long it takes

A clean single geographic number is usually a small number of working days. Larger blocks, multi-site estates and anything involving a system change take longer, and every rejection restarts the clock rather than pausing it.

Ports complete on an agreed date, usually in a defined window. Plan for a short period where inbound routing is settling, and do not schedule it for the morning of your busiest day of the month.

Before the port date

Have the new service built and tested with a temporary number first. When the port lands you want the only change to be which number arrives, not whether the platform works at all.

Point your new trunk at the right destination, check your IVR and out-of-hours rules on the temporary number, and make one test call to every branch. Then let the port complete into a system you already know is right.

What to keep afterwards

Keep the porting confirmation and the final bill from the losing provider. If a call ever routes oddly months later, that paperwork is what resolves it quickly.