There are some simple steps to make sure the configuration works:
The SIP Ports have to match (5060 or what ever you use)
At the far end (radio), you need to forward ports through your router
www.portforward.com will describe how it is done. The manual tells you which ports. (Sip port 5060 udp, 11000 udp, 12000 udp, and the web control port -- your choice ... like 8080 to port 80).
On the Far end (control head), you have to tell that RRC what the IP address is of the far end. You can do this with dyndns, or with the IP address of the far end. Sort of like telling your box which phone number to call.
73, Mike