Motorola Bravo :: Can't Hear Anything During Phone Calls

i have a brand new motorola bravo bought from att (android 2.2). when i make phone calls, i can see the call going out and it even shows 'active call'. but i cannot hear anything and also, the other person cant hear my voice. so, basically, no voice is going in and out during a phone call. same for incoming calls: i can see the call coming and when i accept, it shows 'active call' but no voice is going in and out.

music and Internet work fine. i can hear the phone ring when a call comes. so, fundamentally the phone's sound system works fine.....