IPBX
Asterisk 电话交换机(PBX): http://asterisk.org
SIP
SIP Express Router: http://www.iptel.org/ser
H.323
OpenH323 Gatekeeper: http://www.openh323.org
GNU Gatekeeper: http://www.gnugk.org
OpenH323 代理: http://openh323.sourceforge.net
H323 - ISDN 网关: http://www.telos.de/linux/H323/
会议/VoIP软件
OpenMCU: http://www.openh323.org
类似客户端
XTen: http://www.xten.com
SJPhone: http://www.sjlabs.com/
OpenPhone: http://www.openh323.org
Netmeeting: http://www.microsoft.com