UK phone number portability — keep your number

UK number portability is the rule — set by Ofcom and binding on every UK communications provider — that you keep your existing phone number when you switch to a different network. It's the reason your old 077 EE mobile number can today be on Vodafone, and the reason the Ofcom-allocated Range Holder on a number lookup may not be the current network carrying the line. This guide explains how porting works and what it means for caller identification.

#Why portability exists

Before 1999, switching mobile or landline provider in the UK meant a new phone number. That was a serious friction barrier — losing your business contacts, having to reprint cards, missing calls from old contacts who had the wrong number. Ofcom (then Oftel) mandated mobile number portability in 1999 and landline portability in 1996, with both schemes refined many times since.

By 2026 the practical experience is: switching network is a 24-hour, free, online process. Most customers never see the porting step happen — it's invisible.

#How mobile porting works in 2026

UK mobile porting is handled by the PAC / STAC code system, which became one-text-one-day in 2019:

All three are free, must be returned within 1 minute by every UK mobile network, and are valid for 30 days. You give the PAC to your new provider; they handle the actual port, which completes the next working day.

#How landline porting works in 2026

Since the One Touch Switch scheme launched in 2024, UK landline switching is co-ordinated by your new provider:

1. You sign up with the new provider, telling them you want to keep your number.
2. They contact your old provider electronically to request the switch.
3. Both providers send you a clear 'before you switch' summary (notice period, exit fees, broadband impact if relevant).
4. On the switch date (usually 10 working days later) the line is ported. Your number doesn't change; your old service is cancelled automatically.

#Why portability matters for caller identification

Number portability is the single reason the Ofcom Range Holder shown on a UK number lookup may not be the carrier currently providing the line:

• Range Holder = the provider Ofcom originally allocated the block to (recorded at allocation, never changes).
• Current carrier = the provider currently delivering the line (changes whenever the customer ports). Not published.
• Caller ID network = what your phone displays, usually the most-recent porting carrier — but can be spoofed.

All three can be different for the same number. Example: a number allocated to BT in 2005, ported to Sky in 2015, ported again to a Gamma SIP trunk in 2024. Ofcom still shows BT as the Range Holder, your phone might say 'Sky', and the call is actually delivered over Gamma.

#What you cannot port

A few categories of UK number remain non-portable:

• Pre-pay vouchers without a SIM activation — there's nothing to port.
• Short-code services (159, 7726, 999, etc.) — these are network-routed, not subscriber-owned.
• Some legacy ISDN numbers — being phased out with the PSTN switch-off.
• Numbers in 'quarantine' — recently recovered by Ofcom and held back from re-allocation for typically 6 months.

#Porting and the AI internet check

When you look up a number on this site, the AI internet check is unaffected by porting — it searches the open web for public mentions of the exact digits, regardless of which network currently delivers the call. So a ported number's behavioural reputation (forum reports, business listings, scam-database entries) is preserved across the move. This is one of the reasons the AI check is a useful complement to the Ofcom Range Holder data.

#Bottom line

UK number portability is the reason your number is yours, not your network's. It's also the reason the Ofcom Range Holder data — while authoritative for the *original* allocation — can't tell you the *current* carrier. Use the Range Holder as a starting point, pair it with the AI internet check for behaviour, and remember that the displayed CLI on caller ID is at best the most-recent porting carrier, at worst a spoof.