Safari might support WebRTC in the coming months. Apple appointed 4 members to the WebRTC Working Group: http://www.w3.org/2000/09/dbwg/details?group=47318&public=1

Since the signaling is not part of the standard, on purpose, you can choose whatever you like (XMPP, SIP...) or create you own solution. On the server side, TURN is implemented to go through the NATs, the firewalls, that helps.