Asterisk is a complete PBX and telephony toolkit in software. It runs on Linux, *BSD, MacOSX, and Solaris. It provides all of the features you would expect from a PBX and more as it enables developers to build customized voice applications of many types. Asterisk does voice over IP in many
... [More] protocols, and can interoperate with almost all standards-based telephony equipment using relatively inexpensive hardware. [Less]
Osmocom Media Gateway, to manage, connect and optionally transcode voice streams between different network elements such as BTSs and external entities like SIP. It is typically co-located with both OsmoBSC and OsmoMSC and controlled by them via IETF MGCP (Media Gateway Control Protocol).