When I call my wife on her iPhone 6, my phone randomly mutes during the conversation. The phone will go silent sometimes and it'll last for about 5-10 seconds and then resume. Most times it's when I use the headset. Last night I had a case where I was on speaker with a tmobile rep and it muted me for a good 20 seconds. I could not hear them, but they could hear me. I'm on Android 6.0.1.