A virtual number, also known as direct inward dialing (DID) or access number, is a telephone number without a directly associated telephone line. Usually these numbers are programmed to forward incoming calls to one of the pre-set telephone numbers, chosen by the client: fixed, mobile or VoIP. A virtual number can work like a gateway between traditional calls (PSTN) and VOIP.
Subscribers to virtual numbers may use their existing phones, without the need to purchase additional hardware, i.e. use the numerous available software.
A virtual private number is a telephone number that forwards incoming calls to any of a number of pre-set telephone numbers. These are also called a follow-me number, a virtual telephone number or (in the UK) Personal Number.
Usually a virtual telephone number can be set to forward calls to different telephone numbers depending on the time of day and the day of the week; for example, between 9 and 5 on working days incoming calls will be forwarded to one's workplace, but in the weekends to one's cellphone.
The availability (and acceptable use) of virtual phone numbers is subject to the regulatory situation in the issuing country.
Applications and example of use
Most voice over IP providers offer virtual numbers; unbundled providers label these as "DIDs" (direct inward dial). These are typically offered as local geographic numbers in various selected cities or as toll-free numbers, with the non-geographic number carrying higher per-minute cost to receive calls.
In the North American Numbering Plan, Area code 500 and Area code 533 are follow-me numbers, and referred to as Personal Communications Service (NANP).
In the United Kingdom, these are offered under the 070 non-geographic prefix, referred to as Personal Numbering Service (PNS).