The Vovida Open Communication and Application Library is an open source SIP proxy, registrar, and feature service platform. It includes a number of servers which are tightly integrated and which can provide SIP call control, routing, and SIP features, such as call forwarding and voice mail.
vocalctl(8) vocald(8) sipset(1) rs(1) ms(1) fs(1) vmserver(1) allinoneconfigure(8) vocalconf(5)
More information is available from http://www.vovida.org/