SIPphone: www.sipphone.com

Skype: www.skype.com

SIP Broker: www.sipbroker.com

Google Talk: www.google.com/talk

Vonage: www.vonage.com

Lingo: www.lingo.com

Total Talk: www.totaltalk.com

Asterisk: www.asterisk.org

SIPfoundry: www.sipfoundry.org

GnomeMeeting.org: www.gnomemeeting.org

Damien Sandras的GnomeMeeting博客: blog.gnomemeeting.net

KPhone: www.wirlab.net/kphone

CounterPath: www.xten.net