[Serusers] Totally lost! proxies, firewalls, gateways, etc, etc, etc ...

Hi I'm totally lost I have ser working very well (at least, I think so), with ans_machine (sems), varius exec_dset, numbering, etc, etc, etcBut I Don't know (or found) how to solve the "connectios" troubles For example: Two devices (hard/soft phone) with public IP, NO PROBLEM, works OK On device with public, one with private IP, works some times, NOT allways Two device with private IP, never work :( I know where is the problem (IPs), but I don't know where to find a "soft" solution or a "hard" solution, NOT to expensive Stun server Vovida: I don't like product without docs Some knows other STUN server ? RTP_proxy: I can't understand how it works :( I tested with nat, but I can't understand how it's work For example, how can I choose who will need to use nat helper and who not ? I don't know what other solutions are there Ideas ? Thanks in advance Pablo Murillo