Another thread suggests the same thing:
SIP Trunk problem - NAT - 2 networks - FreePBX / Providers - FreePBX Community Forums
however there is a suggestion that this is done when using chan_sip
Another thread suggests the same thing:
SIP Trunk problem - NAT - 2 networks - FreePBX / Providers - FreePBX Community Forums
however there is a suggestion that this is done when using chan_sip