The phone conference system based on Asterisk software. It supports a wide range of protocols for the handling and transmission of voice over traditional telephony interfaces including H.323, Session Initiation Protocol (SIP) and the Inter-Asterisk eXchange (IAX). This system permits to host phone conferences with no theoretical user limit via IP (SIP/ IAX) and PSTN (phones and mobile phones).
Asterisk is a open source
implementation of a telephone private branch exchange
(PBX) originally created by Mark Spencer