Description:

Asterisk is an Open Source PBX and telephony development platform that
can both replace a conventional PBX and act as a platform for
developing custom telephony applications for delivering dynamic
content over a telephone similarly to how one can deliver dynamic
content through a web browser using CGI and a web server.

Asterisk talks to a variety of telephony hardware including BRI, PRI,
POTS, and IP telephony clients using the Inter-Asterisk eXchange
protocol (e.g. gnophone or miniphone). For more information and a
current list of supported hardware, see http://www.asterisk.org/.