Ekiga is a SIP and H.323 application, supporting audio and video, and is the successor of GnomeMeeting.
Here are some key features of "Ekiga":
ˇ Call Forwarding on busy, no answer, always (SIP and H.323)
ˇ Call Transfer (SIP and H.323)
ˇ Call Hold (SIP and H.323)
ˇ DTMFs support (SIP and H.323)
ˇ Basic Instant Messaging (SIP)
ˇ Text Chat (SIP and H.323)
ˇ Possibility to register to several registrars (SIP) and gatekeepers (H.323)
ˇ Possibility to use an outbound proxy (SIP) or a gateway (H.323)
ˇ Message Waiting Indications (SIP)
ˇ Audio AND Video (SIP and H.323)
ˇ STUN support (SIP and H.323)
ˇ DTMFs support
ˇ LDAP support