VoIP(Voice over Internet Protocol) is simply the transmission of voice traffic over IP-based networks. The Internet Protocol (IP) was originally designed for data networking. The success of IP in becoming a world standard for data networking has led to its adaption to voice networking.

VoIP has become popular largely because of the cost advantages to consumers over traditional telepone networks. With traditional phone service, users in the US pay a flat monthly fee for local telephone calls and a per-minute charge for long-distance calls. On top of that, they usually have to pay a flat monthly fee for Internet connections. Using the Internet connection for both data traffic and voice calls allow consumers to eliminate phone line monthly payment. In addition, VoIP calling plans usually do not charge a per-minute fee for long distance calls within the US and Canada, and have very low international calling rates.

There are three methods of connecting to a VoIP network:

1. Using a VoIP telephone
2. Using a "normal" telephone with a VoIP adapter
3. Using a computer with speakers and a microphone

VoIP telephone calls can be placed either to other VoIP devices, or to normal telephones on the PSTN (Public Switched Telephone Network). Calls from a VoIP device to a PSTN device are commonly called "PC-to-Phone" calls, even though the VoIP device may not be a PC. Calls from a VoIP device to another VoIP device are commonly called "PC-to-PC" calls, even though neither device may be a PC.