Kamailio SIP ServerKamailio is an Open Source SIP Server released under GPL, able to handle thousands of call setups per second. Kamailio can be used to build large platforms for VoIP and realtime communications Ð presence, WebRTC, Instant messaging and other applications. It can also easily be applied to scaling up SIP-to-PSTN gateways, PBX systems or media servers like Asterisk, FreeSWITCH or SEMS.