2.0.7 is feature complete and I am testing for bugs. I hope to have it submitted to Apple in a week. This will be the first release with XMPP jingle VOIP enabled. The voice calling is still not perfect so I have left the Beta label on the button. At the moment it does not use STUN or do any NAT traversal. If both people are on the same network or not behind NAT it will work fine. I hope to fix this in 2.0.8.
The call button will only show up if the other client advertises XMPP jingle audio support.