I have this issue with the 3CX Client on iOS 11: As soon as I setup a call i'm able to receive the audio but unable to speak. 3CX Client mentions : Connected, no microphone. I have tested the same config on 3 other devices (1 pc, 2x Android) and no issue is persistent there. So it's related to my iPhone/iOS setup. I can't find anything related on the community either.