(Voice Over IP) A digital telephone service that uses the public Internet and private backbones for call transport. Support for the public switched telephone network (PSTN) is also provided so that VoIP calls can originate and terminate from regular telephones. Many companies, including Vonage, 8x8 and AT&T (CallVantage), typically offer calling within the country for a fixed fee and a low per-minute charge for international. Customers are required to have broadband Internet access (cable or DSL).|
SIP and H.323
VoIP uses two Internet telephony protocols for handling connections, and most VoIP systems support both (see SIP and H.323).
Regular phones can be used with many VoIP services by plugging them into an analog telephone adapter (ATA) provided by the VoIP provider or purchased from a third party. The ATA converts the phone to IP packets. IP phones can also be used that have built-in IP packet support.
VoIP providers may be entirely softphone based, which requires a computer, phone software and microphone and speakers (or headset) to make and receive calls. Usually free if both sides are on the same service, softphones let users call any phone in the world from their laptops and an Internet connection. Per-minute charges apply to call a regular phone number, but calls from a regular phone may not be possible. In 1995, VocalTec Communications introduced the first VoIP service in the U.S., and it was softphone based (see Internet Phone). See SIP provider.
Voicemail, caller ID, call forwarding and a softphone option (if not a softphone-only service) are typically part of a VoIP package. Phone numbers with area codes outside of one's own home area may also be an option (see virtual phone number). See IP telephony for more details and history of the technology.