When i make calls my phone now has a weird symbol on the screen. It's a black rectangle with little white + signs diagonally across the rectangle- separating the rectangle into a blue half and a black half.
You can change this option either while on a call by pressing the menu key and then Enhance Call Audio, or you can go into your call history (press the call button from the home screen), press the menu key, select Options, and then General Options. The enhance call audio options are at the bottom of the list.