Ekiga (formely known as GnomeMeeting) is an open source VoIP and video conferencing application for GNOME. Ekiga uses both the H.323 and SIP protocols.
Gizmo Project uses your internet connection (broadband or dial-up) to make calls to other computers. connected to friends, family, and colleagues anywhere on earth. It's just that simple. Supported on Treo 600/650/680/700p/755p, Sony UX-50, all Palm Tun