Hello,
I am so sorry for a question that could be evident for an expert. Our normal IPBX responsible as gone away since one year, and due to a machine crash, I’m in charge to reinstall all the system.
I succed to do all the job 
, except working with an external IP. The hardware is the same (Livebox pro V4 + Antec computer). All software has been upgraded in last versions (Sangoma disto + FreePBX).
When I use a SIP Phone connected on our LAN, using 192.168.1.115:5160 as the adress of the SIP server, the status of the phone (displayed in the web interface of the phone) is immediately set to “Registered”, and it work perfectly.
But when I try to use our public IP address (80.12.80.xxx - As it is the only parameter to be changed, it ensure that there is no password problem), in order to connect users not connected to our LAN, the status of the phone is “Trying”, then “Waiting delay”. When I try to compose an internal number, or an external, the result is the same, I hear the busy tonality.
When using intentionnaly a wrong password with internal IP 192.168.1.115, the server answer “403 error”. When I use a wrong password with the external IP, the server’s answer is the same (“Trying”, then “Working delay”). It seems that the call do not reach the server.
In the NAT/PAT table of our box, the former responsible have done this for FreePBX :
Port 1194 : TCP and UDP
Port 4443 : TCP
Port 4569 : UDP
Port 5038 : TCP and UDP
Port 5061 : UDP
Port 5160 : TCP and UDP
Port 5161 : UDP
Ports 10000-20000 : UDP
I tried to put freepbx in a DMZ on our box, and I disabled FreePBX Firewall for a few minutes, but the result is the same, busy tonality. So it seem it is not a firewall problem.
I am at the end of the ideas I can have, and would be greatly happy with all other suggestions…
All the best,
Etienne