yes, that´s possible. If you use "simple" H.323, you don´t need any SIP or SfB-Server. At this point your Group is reachable via normal IP, that means your remote peer is able to contact you calling your public IP and vice versa. Of course you´ll have to do a bit of work on your firewall (open ports, set NAT, etc.), but after that you can do P2P IP calls, no problem.
I think here and in the FAQs you´ll find enouigh information how to handle this. ;-)