Mitel - Business Communications and Collaboration
Asterisk - An open source telephony switching and private branch exchange service for Linux.
Eir SIP Voice - eir SIP Voice is revolutionizing the core communications tool of business that carries both calls and data over just one connection.
FreeSWITCH - FreeSWITCH is an open-source media application designed to support popular protools such as SIP and WebRTC and provides a platform to develop voice and video applications.
Phonebooth - Phonebooth is one of the leading voip providers, providing phone systems & phone service for small businesses.
FusionPBX - FusionPBX is an open source FreeSWITCH GUI.