I'm with you on this one Bloggs. I know the things auto-mute and that's all fine and dandy but ive seen guys zone out completely whilst lost in the loving embrace of some elevator music.
Last week I discovered a pilot I was training was using his iPhone to listen to music whilst we were cruising along at FL180. I wondered why he had a blank look on his face and kept asking me to repeat what I was saying. Needless to say, next time he pulls that stunt both him and the phone will be down the back and neither will be sharing the front row of the aircraft again!