Opensource Asterisk is complete telephony PBX that run on Linux (Recommended), BSD and MACOS Proxy all telephony features that you expect from a PBX beside a lot of other features. Asterisk maybe can use on all major operating system Asterisk™, the Open Source PBX, is taking the world by storm. Asterisk makes a complete business- or carrier-class PBX out of an ordinary Linux computer, integrating with the telephony network as well as the new world of voice over IP and Internet..
Asterisk does VoIP in any protocols and can interoperate with almost all standards-based telephony equipment using relatively inexpensive hardware Asterisk needs no additional hardware for VoIP. For interconnection with digital and analog telephony equipment, Asterisk supports a number of hardware devices, most notably all of the hardware manufactured by Asterisk’s sponsors, Digium. Asterisk supports a wide range of TDM protocols for the handling and transmission of voice over traditional telephony interfaces. Asterisk supports US and European standard signaling types used in standard business phone systems, allowing it to bridge between next generation voice/data integrated networks and existing infrastructure. Asterisk provides a central switching core, with four APIs for modular loading of telephony applications, hardware interfaces, file format handling, and codecs. It allows for transparent switching between all supported interfaces, allowing it to tie together a diverse mixture of telephony systems into a single switching network.