Frog Hello, I'm a voip specialist with 10+ years of experience working on the TS/NOC departments of a US VoIP company; I can install, troubleshoot and customize many VoIP devices including: softphones, ATA's, IP-phones and PBX systems like Asterisk/FreePBX. I read your project description and I can help you troubleshoot your connectivity issue, the problem you described could be many things, this will require extensive testing, network testing/analysis, sip packets analysis and possible other techniques, to find out the main cause of the problem, then come up with a solution. You may contact me through chat to discuss this project further.
Thank you.