Hello,
Hope you are doing well.
I have gone through the project you just posted with name of - voip android with required skills of Android, Asterisk PBX, Mobile App Development, VoIP, XMPP.
As per my understanding I have understood the project and I can complete it for sure.
Any requirement document or any website link you have for this project?
But before going forward I would like to discuss few things with you on chat and I hope that is fine with you. I am waiting for your ping on chat.