Move your UK phone numbers to NumberGroup.
Free. Seamless cutover. We drive it all.

The 4-step process

1. 1
   You sign one authorisation

   Day 1

   Enter your website domain — we auto-fill your company name and address straight onto the one-page form. List the numbers you want to bring. Sign on screen. Valid 6 months. That's the only paperwork you do.
2. 2
   We submit the transfer request

   Days 1–3

   We file with your current carrier through BT Wholesale's regulated interface, and start building your call routing on our network so it's ready ahead of the port date. If a downstream supply chain exists (your reseller buys from a wholesaler, who buys from a carrier) we route through the right communications provider for you — note that each extra link in that chain can add a few working days, as every party has to action their part. We'll come back with a confirmed transfer date 48–72 hours later.
3. 3
   The port activates — and your calls are already with us

   Port day

   Here's why it's seamless: before the port date, we've already built your call routing on our network — your numbers, ring groups, mobiles, SIP, voicemail-to-email, all configured and standing by. So when BT Wholesale activates the port on the agreed day, the path to deliver your calls is already live. They simply start arriving with us. There's no gap where calls fall into a void. We watch the activation happen in real time.
4. 4
   We confirm it's live, then you cancel the old service

   After

   Once calls are routing through us we confirm with you, and keep watching for 24 hours. Routing rules you set up before the port are already working. Only THEN do you serve termination notice on your old provider with the correct notice period — never before, because cancelling first risks losing the number.

What you need to send us

• Company name exactly as it appears on your current phone bill (legal entity, not trading name unless trading name is on the bill)
• Billing address from the current bill
• List of numbers to bring — either in a paste, a screenshot of the bill, or the carrier export
• Main Billing Number (MBN) for geographic numbers, if you know it (often on the first page of the bill)
• Site address for each number if you have multiple physical sites
• Authorised signatory — typically the company director, IT manager, or whoever signed the original telecoms contract

We turn all of that into the CLoA for you, then a one-page summary of what's about to happen. Same-day.

If your old provider tries to block it

They can't — but they will sometimes try. We've seen all of it. Here's what each looks like and what we do:

Big estates: 50+ numbers, multiple sites

We do estate transfers regularly — multi-site retailers, contact centres, professional-services firms with multiple offices. The principle is the same; the coordination is bigger. Two things change:

• Pre-transfer audit. We send a senior transfer engineer to walk through your current setup — every line, every non-voice device (alarms, lifts, EPOS), every dependency — before any form is signed. Free.
• Phased cut-over. We don't move everything at once. Critical numbers go first (typically your main hunt-group destination), then we move outward over 1–2 weeks. Each phase has its own cut-over window.

Things buyers ask before transferring

• How long does it take to transfer a UK phone number to NumberGroup?
  It depends on the type and size. A single line is usually ready in about a week (BT's minimum lead time is 4 working days). Most business numbers — a number plus a few DDIs — complete in 10–15 working days. Larger estates (150+ lines or complex DDI ranges) run to 17–22 working days, and a number that has been ported between providers before adds roughly another 3 working days. We drive the entire timeline as your gaining provider — you don't have to chase anyone — and you'll get a confirmed transfer date 48–72 hours after the request is accepted.
• Does NumberGroup really transfer my numbers for free?
  Yes. NumberGroup Membership absorbs BT's wholesale per-number transfer fee (which ranges £2.49 to £116 depending on type and supplier) — there's no cost to you. We do this because we want you to move all your numbers across in one cut-over, not piecemeal. If you have a complex estate (50+ numbers, multiple sites, mixed providers), we'll do a free pre-transfer audit before quoting.
• Will my phones go down during the transfer?
  No, if it's done correctly — and we do it correctly. The reason it's seamless is that we build your call routing on our network in advance, before the port date. So when the number actually activates on the agreed port day, the path to deliver your calls is already standing by — they simply start arriving with us. There's no separate 'switch-on' gap where calls fall into a void. We watch the activation in real time and confirm with you once it's live.
• What form do I have to sign?
  A one-page authorisation — technically a CLoA (Customer Letter of Authority). On numbergroup.com/porting/start you enter your website domain; we pull your company name and registered address straight from public records and pre-fill the form for you. You just list the numbers, sign on screen, and we take it from there. Valid for 6 months.
• Can my old provider block the transfer?
  No. UK number portability is a legal right under Ofcom's General Conditions — number portability sits in Condition B3 (a provider can't delay a port by more than one business day), and your switching rights are in Condition C7. Every UK communications provider must release a number when properly requested. The losing provider can flag legitimate issues (mismatched account name, unpaid balance currently in dispute) but cannot refuse outright. We've seen everything: providers stalling, providers pretending the request didn't arrive, providers quoting fictional charges. If your old provider tries any of this we escalate through Ofcom's CP channels and the transfer still completes.
• Do I need to cancel my old contract before transferring?
  No — and you shouldn't. The transfer and the contract are independent. Transfer first, confirm the number is live on us, THEN serve your termination notice with the correct notice period. Cancelling first risks losing the number, because once the line is ceased the transfer path closes. You may still pay out any remaining contract term to your old supplier; that's a billing matter between you and them, and is unrelated to the transfer.
• What can go wrong with a UK number transfer?
  Four common issues, all preventable: (1) the company name on the authorisation form doesn't match the name on the current bill — we pull from Companies House so this is rare, but check it before signing; (2) account in active dispute with the old provider over an unpaid balance — settle the disputed invoice first or document the dispute; (3) request submitted during a critical trading period like Christmas Eve — schedule outside critical windows; (4) hidden non-voice equipment on the line (alarms, lift phones, EPOS terminals) that nobody told us about — we ask up-front in the audit. Run a 15-minute pre-transfer walkthrough and these all disappear.
• Can I keep my geographic number if I move offices?
  Yes — that's exactly what portability protects. UK geographic numbers (01/02) are technically tied to an area code but the regulated transfer process lets you take them anywhere. We can move a 020 London number to a business that's now in Edinburgh, a Manchester 0161 to a home worker in Cornwall. The caller still pays the call cost for the geographic prefix; you keep the number for life.

Want the deep-dive? Read the porting guide on our blog for the full Ofcom General Conditions explainer, IPEX overview, and worked example timelines.