how can i connect two pbxs each has its public ip address using freepbx. I want to use sip protocol. I’m behind nat. Do i have to use any commercial sip trunk to achieve that?
For Asterisk, I don’t understand the problem. Provided all the PBXes, except Asterisk, are outside the NAT, there is nothing special at all.
If this is related to a limitation of FreePBX, you need to ask on a FreePBX forum.