Quick answer
Number porting is moving your existing phone numbers from your current provider to a new one, and in the UK it is a regulated right: your provider must release your numbers when you leave. Business landline numbers (01 and 02), non-geographic numbers (03, 08, 09) and whole DDI ranges all port to a hosted telephony platform or a SIP trunk. The new provider manages the process; you sign a letter of authority, they submit the request, the losing provider validates it, and a port date is agreed. Single lines typically complete in one to two weeks, ISDN and DDI ranges in two to four, with the actual transfer taking minutes on the day. Porting is often free or a small per-number fee. The golden rule is that the new system is live and tested before the port date, so the handover is a switch rather than a gap.
I have managed a lot of ports and the ones that go wrong share a cause: a detail on the bill that nobody checked. This guide covers what can be ported, the timescales, what to check first and the failure modes. If you would like the port managed as part of a move to hosted telephony, get a no-obligation quote.
What can be ported
| Number type | Ports to hosted / SIP? | Notes |
|---|---|---|
| Geographic landline (01, 02) | Yes | The standard case. Ports as a single line or as part of a range |
| DDI range on ISDN | Yes | The whole range ports together; ask whether it is charged per number or per range |
| Non-geographic (03) | Yes | Ports between providers like a landline; increasingly common for business main numbers |
| Freephone (0800, 0808) and 084/087 | Yes | Ports via the number's range holder; can take longer and cost more; check the tariff implications |
| Premium rate (09) | Yes, with conditions | Specialist; confirm early |
| Numbers on a bundled product (e.g. line plus broadband) | Usually | Separating the number from the bundle can affect the broadband; plan the connectivity first |
| Very old numbers on legacy products | Usually, with care | Occasionally need an intermediate step; the new provider will know |
Mobile numbers port too, using a PAC code, but that is a separate process covered in our business-mobile guides.
How the process works
- Gather the paperwork. A recent bill from the losing provider showing the exact numbers, the account name and address, and the account number. This is the step that decides whether the port sails through or bounces.
- Sign a letter of authority. This authorises the new provider to act on your behalf. It must match the bill exactly - same legal entity name, same address.
- The new provider submits the request. They send the port order to the losing provider (or the range holder), specifying the numbers and a proposed date.
- Validation. The losing provider checks the details against its records. If everything matches, the port is accepted and the date confirmed. If not, it is rejected with a reason code and resubmitted once the detail is corrected.
- Build and test the new system on temporary numbers in the meantime: call flows, voicemail, handsets, apps, recording. Everything should be working before port day.
- Port day. At the agreed time the number's routing switches from the old provider to the new one. Calls start arriving on the new system within minutes. Test inbound and outbound on every ported number.
- The old service ends. With the numbers gone, the losing provider ceases the line, or you give notice on the remaining contract. Check the final bill.
How long it takes
As a working guide: a single geographic line typically ports in one to two weeks from a clean submission. ISDN2 and ISDN30 with DDI ranges typically take two to four weeks, partly because the losing provider has more to validate and partly because complex ports are scheduled rather than automatic. Non-geographic numbers vary by range holder, from a couple of weeks to longer. A rejected submission adds a week or so each time, which is why the bill check matters. Providers agree a port date in advance, so you know when the switch will happen and can plan around it.
What it costs
Porting is often included in a hosted telephony contract; where it is charged, expect a small one-off fee per number or per DDI range. A large porting charge is a negotiating point. There is no ongoing cost specific to ported numbers beyond the normal per-number rental, usually pennies a month. Our hosted telephony pricing guide puts porting in context with the other one-offs.
Why ports get rejected, and how to avoid it
Almost every rejection is a data mismatch: the company name on the letter of authority differs from the account name on the bill (Ltd versus Limited, a trading name versus the legal entity), the postcode is the billing address rather than the installation address, a number on the range was missed or included wrongly, or the account has an outstanding order or dispute on it. The fix is boring and effective: work from the most recent bill, copy the details exactly, and have someone who knows the account check the list of numbers before submission.
Two other traps. Ceasing the old service too early: if you cancel the line before the port completes, the number can be released back into the pool and become very hard to recover. Let the port take the numbers; the line ceases afterwards. Bundled products: if your broadband rides on the phone line you are porting away, the broadband can stop when the number leaves. Sort the connectivity - SoGEA or full fibre - before the port. This is one of the sequencing points in the PSTN switch-off that catches businesses out.
Porting and the switch-off
The ISDN and analogue switch-off means every business with a copper line will port its numbers at some point before 31 January 2027. Left late, ports queue up behind everyone else's. Done in your own time, the port is a quiet Tuesday morning switch. Whether you move to hosted telephony or to SIP trunking into your existing PBX, the porting process is the same.
The bottom line
Your numbers are yours to take. Porting to a hosted platform or SIP trunk is routine, it is your provider's job to run it, and it goes smoothly when the paperwork matches the bill and the new system is tested before port day. The two things not to do are cease the old service early and leave it until the switch-off deadline makes the timetable for you.
We manage porting as part of every move: get a no-obligation quote or call 0333 006 9399. Our hosted telephony service page explains where porting sits in the install.
Not sure who is calling one of your numbers? 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.
Frequently asked questions
Can I keep my business phone number if I switch to VoIP?
Yes. UK landline, non-geographic and DDI numbers all port to a hosted telephony platform or SIP trunk under Ofcom's porting rules. Your existing provider must release them when you switch. The new provider manages the process.
How long does business number porting take in the UK?
Typically one to two weeks for a single landline and two to four weeks for ISDN and DDI ranges, from a clean submission. Non-geographic numbers vary by range holder. The transfer itself happens within minutes on the agreed port date.
Does it cost anything to port a phone number?
Often nothing; otherwise a small one-off fee per number or per DDI range. Ported numbers then cost the normal per-number rental, usually pennies a month. Query any large porting charge.
Can I port an 0800 or 03 number to hosted telephony?
Yes. Non-geographic numbers port between providers via the range holder. 03 numbers behave like landlines; 0800/0808 and 084/087 numbers can take a little longer and may have tariff implications worth checking.
Why was my number port rejected?
Almost always a mismatch between the details submitted and the losing provider's records - company name, address, account number or the list of numbers. Correct the detail against the most recent bill and resubmit. Open orders or disputes on the account can also block a port.
Will my phones stop working during the port?
They should not. The new system is built and tested on temporary numbers first; on port day the routing switches in minutes and calls arrive on the new system. The old line is ceased afterwards. A short overlap where both systems ring is normal and harmless.
Should I cancel my old phone contract before porting?
No. Cancelling or ceasing the line before the port completes can release the numbers back into the pool. Let the port move the numbers first, then give notice on whatever remains of the old contract.