Well i got a call and picked up my pre and what do u know!  I could hear nothing and they could hear nothing.  So after a min i noticed the little headset icon on the dial pad insted of the speaker thing or whatever it is.  I was pissed at first.  lol.  The phone was stuck in headset mode.  I tried resets and messing with the headset jack etc.  nothing worked.  So i went to the sprint repair center thinking i was getting my 4th pre.  And they fixed it!  He said its some kind of software glitch.  He said he completed a call with it not working then he plugged in the headset made a call and unplugged it during the call then he put it on speaker phone and when he hung up the phone was working again.  lol.  yea so just beware.