SIP connections

Hi, there!

Intenting to do VoIP connections and Pc-To-Phone (PSTN) calls, I have some doubts.

1. Is there possible to estabilish SIP connections through AIR?

2. If yes, which would be the path? If not, I would like to know what in fact is Ribbit Phone (www.ribbit.com) if not a way to do VoIP calls.

3. Is there possible to integrate LIB, .CAB or .OCX functionallities to my AIR application?

Thank you,
CaioToOn!