Gizmo is a free software which is more like a "Free PC Phone". The major advantage of Gizmo is that it works on Linux and it offers Voice Chat with multiple protocols (Yahoo, GTalk, Windows Live and more), option which in the traditional IM's for Linux (Kopete and Gaim) is not implemented ...yet ;) Here you cand find more about this software: http://www.gizmoproject.com/index.php