Voice over IP (VoIP) alows voice to be transmitted using TCP/IP protocols, usually over the internet. In the context of Amateur radio, there's usually a radio on one end of this somewhere. VoIP can be used to connect users without radios, a user without a radio and a radio without a user, or even two radios. The radios can be VHF, UHF, or even HF.
One of the reason these technologies are so popular for amateur radio operators is because it lets licensed technician class operators talk around the world without having an HF license. It is also handy to check into club Nets when out of town.
 Amateur radio VoIP protocols and nets
The following VoIP Amateur radio networks exist:
- unix and windows support; PC client available
- requires $150 interface board; linux support only; repeaters only, no PC client
- same protocol as echolink; no central server??
- popular in Europe
- Yaesu proprietary linking protocol; very flexible interface; windows only; no third party support; requires $180 interface board
- Allstar link
- linux / asterisk based linking system
 EchoLink and IRLP
- http://www.echoirlp.com/ software to bridge EchoLink and IRLP; includes a very good list of other ham VoIP software
- http://cqinet.sourceforge.net/ TheBridge and EchoLinux
- javecho java echolink client