I have the same problem with my xperia Z. I know that it is a **bleep**ty hardware problem as when my earpiece gets dead i jerk my phone and tap it on my hand one or two times and it gets right. I dont know for how long this tapping will work. Plzz help before it gets permanently dead.
Sony should also take this problem seriously and should reply to these threads themselves for their customers. It seems like sony doesnt give a dam **bleep** about all this............!!!!!!!!!!!!!!!!!!
