Hi, I have read the details I believe I can do this job. While I believe I have some queries which need to be clarified. For that I would request you to start the chat so we could clarify those I have good experience with iPhone, Asterisk PBX, Mobile App Development, Server, Google Firebase, Linux, Software Architecture, SIP and Android. We can discuss the timeline and budget after that. You can see all my skills, experience, customer reviews and relevant jobs from my profile.
My portfolio: https://www.freelancer.com/u/AITSoft
Shamshad