Android-iOS VOIP Voice Call App

We are currently working on our mobile application, GCM Dialer, which handles both SIM and SIP calls. We have successfully implemented the conference screen for the SIM and SIP merge option, but we are encountering an issue where voice is not being exchanged between all parties... (Budget: ₹1500 - ₹12500 INR, Jobs: Android, Asterisk PBX, Audio Processing, iOS, Mobile App Development, Mobile Development, Signal Processing, SIP, Telecommunications Engineering, VoIP)