I have a FreePBX 188.8.131.52 running on a Rasperry Pi and am actually very happy with this phone system. I have two SIP trunks going to the internet and probably my firewall gets a bit confused with the outgoing UDP connections. The first SIP trunk can still be registered without problems and with the second one no UDP packets come back from the SIP server. Probably these are blocked by the firewall.
Now my question is: how can I change the soure port of the UDP connection in the SIP trunk?