Who Uses DIDs?
VoIP DID providers offer wholesale DID VoIP provisioning services to businesses such as:
- Wireless phone companies
- Calling card companies
- VoIP service providers
A direct inward dialing (DID) number is a unique phone number.
Some DID providers also offer virtual number provision directly to individual businesses and consumers. DID VoIP services to consumers offer the opportunity to buy low-volume or even single virtual numbers in numerous domestic and international calling areas, so that far-flung customers, friends, and family can call local numbers for little or no cost. Those virtual numbers can then forward calls to a variety of terminal choices, including:
- Skype/VoIP/Google Talk numbers/phones
- Cell phones
VoIP DIDs can also support a number of different protocols, such as:
Traditionally, DID providers were competitive local exchange carriers (CLECs) and offered volume DID purchasing only to large-scale carriers such as AT&T and Sprint. More recently, with the increase in small-scale hosted VoIP providers, many VoIP DID providers are offering DID VoIP service with no minimum purchase.
Still other DID VoIP providers such as VoIP Innovations provide sophisticated VoIP DID management as well as provisioning. Recognizing another business opportunity, these types of VoIP DID providers may even offer a wide variety of ways to choose DIDs beyond the rate center availability, such as by:
- Network (carrier, CLEC, reseller)
- Feature (T38, CNAM)
DID VoIP providers may also offer the option to purchase DID service by the minute or port, and to incorporate add-on features such as e911, 411, and CNAM (calling name, used for services such as caller ID).
Many DID VoIP providers also offer online DID ordering with very fast — if not immediate — provisioning.
How DIDs Work
A direct inward dialing (DID) number is a unique phone number. An example would be your home phone number, an 800 number, or any of a company's individual phone numbers (not extensions). A phone number is an ID of sorts, and is used to connect to and use the publicly switched telephone network (PSTN).
Residential phone numbers are associated with a pair of wires coming into the home. In businesses with multiple numbers, having each unique number tied to a pair of wires is a logistical nightmare.
DIDs (or DDIs, for direct dial-in, through much of Europe and the South Pacific) evolved as a way of supporting multiple numbers on a small amount of physical lines. DIDs were developed by AT&T in the 1960s, as businesses started relying on private PBXs rather than the telephone company's PBX service. AT&T modeled the organizational system on the German post office's system. DIDs — a local geographic or national telephone number — are used in conjunction with a company PBX, which routes calls internally.
Businesses use a local PBX with a trunk supporting multiple lines, or phone numbers. The trunk is assigned a range of numbers, or DIDs. The PSTN sends calls to those numbers to the trunk, which sends them on to the PBX. The PBX identifies the dialed destination number (DNIS) and sends the call to the right extension. VoIP DIDs use a gateway between the trunk and the PSTN.