VoIP numbers UK — what they are, 056 vs 020

VoIP (Voice over Internet Protocol) numbers are UK telephone numbers where the call is delivered over the public internet rather than a traditional copper or fibre telephony circuit. In 2026, the majority of UK landline calls are VoIP under the surface — BT's full PSTN switch-off completed in early 2027, with all remaining copper voice services migrated to VoIP. This guide explains what a UK VoIP number actually is, the two ways VoIP numbers are presented (geographic or non-geographic), and how to identify a VoIP caller.

#What 'VoIP number' really means in the UK

Strictly, every UK phone number is just a string of digits. Whether a call to that number travels over copper, fibre, ISDN, mobile radio or VoIP is a question of how the call is delivered, not what the number itself is. So 'UK VoIP number' is a slightly loose term that's used in two distinct ways:

1. 056 — location-independent VoIP range. Ofcom's dedicated 056 prefix is explicitly reserved for VoIP and other location-independent services. A 056 number is always VoIP-delivered by definition.
2. Geographic numbers (01 / 02) hosted on VoIP. Any UK landline-shaped number (020 7946 0000, 0121 496 0000, etc.) can in fact be delivered over the public internet — and after the PSTN switch-off in 2027, nearly all of them are.

#How to tell a UK VoIP number when you see one

Without making a technical call-trace, you usually can't be sure whether a specific UK number is currently VoIP-delivered. But there are strong hints:

#What VoIP numbers cost to call

Cost depends on the dialled prefix, not on the delivery technology. Calling a UK landline-shaped number that happens to be VoIP-delivered costs exactly the same as calling a copper-delivered landline of the same prefix:

• 01 / 02 geographic VoIP → 01/02 landline rate, in mobile bundles.
• 03 (0303 / 0330 / 0333 / 0345) non-geographic VoIP → 01/02 rate, in mobile bundles.
• 056 location-independent VoIP → 01/02 rate, in mobile bundles. See 056 numbers UK.
• 0800 / 0808 VoIP-routed freephone → free for the caller.

VoIP delivery saves the *receiving* business money (no PSTN line rental) but is billed to the caller exactly like a normal landline call.

#Who uses UK VoIP numbers

Almost everyone, increasingly. Specific patterns:

• Distributed UK businesses — a 020 London number routing to a contact-centre in Manchester or Cardiff (or abroad).
• SaaS support desks — a 0203 number on a Twilio or Vonage SIP trunk.
• Charities and small offices — Voicehost / Voipfone hosted PBX with a vanity 0203 or 0117 number.
• Modern startups — usually 0330 or 0333 on a VoIP backbone.
• Post-PSTN-switch-off landlines — every former copper landline in the UK by 2027.

#What is a SIP trunk?

A SIP trunk is the wholesale VoIP equivalent of an ISDN line: a virtual circuit that carries multiple concurrent VoIP calls between a business's PBX and a wholesale carrier. UK SIP-trunk providers include Gamma, BT Wholesale, Vonage Business, Voicehost, Voipfone, Magrathea, Daisy and Andrews & Arnold. Most modern UK business phone systems run over SIP trunks rather than ISDN.

#VoIP vs landline — what's the difference for me?

From a caller's perspective in 2026: none, in practice. Cost is the same, voice quality is usually better on VoIP, the number works exactly the same way. From a business perspective, VoIP is cheaper and more flexible (work-from-anywhere, easier call recording, easier integration with CRM). From a 999 perspective, VoIP lines must support emergency calls and provide location data to operators under Ofcom rules.

#Bottom line

Most UK landline calls in 2026 are VoIP under the surface. The numbering hasn't changed — 020 is still 020, 0121 is still 0121 — only the delivery technology. For dedicated VoIP-only numbers, look for the 056 prefix. To identify a specific UK number, paste it into the lookup form on the homepage and see the Range Holder.