FreeSWITCH is an open source telephony platform designed to facilitate
the creation of voice and chat driven products scaling from a soft-phone
up to a soft-switch.  It can be used as a simple switching engine, a
media gateway or a media server to host IVR applications using simple
scripts or XML to control the callflow.

FreeSWITCH supports various communication technologies such as SIP, H.323
and GoogleTalk. This makes it easy to interface with other open source
PBX systems such as sipX, OpenPBX, Bayonne, YATE or Asterisk. It also
also support both wide and narrow band codecs. This makes it an ideal
solution to bridge legacy  devices to the future. The voice channels and
the conference bridge module all can operate at 8, 16 or 32 KHz
and can bridge channels of different rates.