How UK virtual phone numbers work
A virtual number is an ordinary phone number that is not tied to a physical line. What matters is what happens to a call after it arrives — and the answer differs between providers.
The number
A UK geographic number (starting 01 or 02) is allocated to a telecoms carrier, which hosts it on its network. In the industry this is called a DID (direct inward dialling) number. To a caller it is a normal UK landline number, charged as one.
The first leg: the incoming call
When someone dials the number, the call travels over the public switched telephone network (PSTN) to the carrier hosting it. That is the first call leg.
Delivering the call — three common models
- To an app or internet phone. The provider delivers the call over the internet to an app or SIP device registered to the account. For BluePhone, this means creating a second, internal call leg addressed to the account’s app and bridging it to the incoming call when the user answers.
- Forwarding to another phone number. The provider answers the call and dials a second telephone number — typically the customer’s mobile — then joins the two calls.
- On a SIM or eSIM. The number is attached to a mobile line, so the call arrives through a mobile network.
All three involve more than one network or call leg somewhere. The practical differences are what device answers, whether another telephone number is dialled, and what the user needs — an app, a SIM slot or eSIM, or nothing.
Why the distinction matters for prison calls
The HMPPS policy framework tells prisons to restrict “numbers linked to call diversion and re-routing services” without defining those terms. Being precise about which model a service uses helps staff apply the policy to the facts. BluePhone uses the first model and does not dial any other telephone number. Read about the policy.
- Prison telephone system → public telephone networkThe prisoner dials the customer’s UK geographic number. This is an ordinary inbound call on the public switched telephone network (PSTN).Leg A · PSTN, inbound
- Customer’s 01/02 number, hosted by BluePhone’s carrier (Telnyx)The number is dedicated to one BluePhone account. The carrier notifies BluePhone’s servers; the inbound call is held, not yet answered.
- BluePhone serviceLooks up the account that owns the number (the subscription must be active), wakes that account’s app, and starts a second call leg addressed to that account’s own SIP identity — not to a telephone number.Leg B · SIP address, created by BluePhone
- Customer’s signed-in BluePhone appThe app receives leg B over the internet (WebRTC). When the customer answers, BluePhone answers leg A and bridges leg A to leg B. If either side hangs up, the other leg is ended.Bridge · leg A ↔ leg B
Questions
Is a virtual number a real phone number?
Yes. It is a normal UK number that anyone can dial. It is simply hosted by a carrier rather than tied to a copper or fibre line at an address.
Does a virtual number forward calls to my phone?
It depends on the provider. Some forward calls to another phone number. Others, including BluePhone, deliver the call to an app over the internet instead of dialling another number.
Do callers know the number is virtual?
A geographic virtual number looks and is charged like any UK landline number. Prison staff may ask about a number when checking it, and the honest answer is always the right one.
Related guides
Get your own UK number
£15/month or £149/year. iPhone and Android. No eSIM required. Incoming calls only. The prison decides whether to approve the number.
