Hi,
Already did that and activated debug. Interestingly, nothing shows in the log. I have a feeling that Fring has an embedded STUN request (I didn't try sniffing packets on the net at my end at this stage).
May I suggest something you can try if your system allows it?
Either:
1. Install a SIPproxyd on your network and configure it to forward requests to your 3cx SIP server.
or
2. Make sure you have an external dns-to-real IP service running (Like DYNDNS.org for example), then Under 'General' --> 'General Settings' tab, select 'Settings for Direct SIP Calling', tick the Allow calls to domain and set your DNS resolvable name in the Local SIP domain, then set the external DNS resolvable name in the 'proxy' field in your Fring settings.
Cheers,
W.