KphoneSI (kpsi) is a SIP (Session Initiation Protocol) user agent
for Linux, with which you can initiate VoIp (Voice over IP) connections
over the Internet, send Instant Messages, subscribe your friends
presence information and start other applications of your choice
Session Initiation Protocol (SIP) [1] is fast becoming the protocol of choice for IP based communication
– specifically telephony (Voice over Internet Protocol - VoIp), video, and instant
messaging.
