Hello, I'm a voip specialist with 10 years of experience working on the level2/NOC department for a US voip company; I can install, troubleshoot and customize many sip devices including: softphones, ATAs , IP-phones and PBX systems like Asterisk/FPBX. I read your project description and I reviewed your kamailio setup, and I may be able to help, I compared it with my working kamailio setup that has webrtc enabled and I see some small differences, I could do some troubleshooting to pin-point what is wrong. You may contact me at any time so we can go through more details.
Thank you.