Asterisk™ is a complete PBX . It runs on Linux and provides all of the features you would expect from a PBX and more. Asterisk™ does voice over IP in three protocols, and can interoperate with almost all standards-based telephony equipment using relatively inexpensive hardware.

Asterisk™ provides Voicemail services with Directory, Call Conferencing, Interactive Voice Response, Call Queuing. It has support for three-way calling, caller ID services, ADSI, SIP and H.323 (as both client and gateway).

Asterisk™ needs no additional hardware for Voice over IP. 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. Digium has single and quad span T1 and E1 interfaces for interconnection to PRI lines and channel banks as well as a single port FXO card and a one to four-port modular FXS card.

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 signalling types used in standard business phone systems, allowing it to bridge between next generation voice-data integrated networks and existing infrastructure. Asterisk™ not only supports traditional phone equipment, it enhances them with additional capabilities.