Hello Firefox, this is Chrome calling
We are in the process of adding persistent chat and conferencing to Twelephone (<a href="http://twelephone.com" rel="nofollow">http://twelephone.com</a>).  These features, in addition to our existing audio/video calling and presence using Twitter as a directory service, should put our free service near feature parity with Skype.  We're using HTML5 WebRTC with encrypted peerconnections and soon datachannels.  Stay tuned...