) A digital telephone service that uses the Internet for transport, as well as private IP networks. "IP" stands for "Internet Protocol." In order that calls can originate and terminate from regular telephones, connections to the public telephone network (PSTN) are also provided. Telephone companies, cable companies and dedicated providers offer VoIP calling for a fixed monthly fee or low per-minute charge. Customers must have Internet access.
Telephony Protocols: SIP/H.323 and Skype
VoIP uses two telephony protocols for handling connections (see SIP
), and most VoIP systems support both. Skype uses its own protocol (see Skype
All IP handsets plug directly into the Internet, and a large variety of native IP desk and cordless phones are available. Traditional analog phones can also be used by plugging them into an analog telephone adapter (ATA), which converts the analog signals to IP and vice versa (see analog telephone adapter
Software Only = Softphone
VoIP may be entirely software based, which uses an app in a mobile device or a computer equipped with microphone and speakers. Typically free if both sides are on devices; calls to a regular telephone are per minute. In 1995, VocalTec Communications introduced the first VoIP service in the U.S.; entirely software based (see softphone
). Skype is a very popular softphone-based VoIP service (see Skype
). See SIP provider
Along with other features, voicemail, caller ID, call forwarding and a softphone option 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.