[TurboFool]

The circle, itself, isn't buttons. Only the face around the circle is a button (or two buttons, to be more accurate). When you're pressing in a direction, you're actually pressing that entire half of the face of the phone, and the touch-sensitive surface is registering where your finger is when you click the button to determine the function. If your finger's on the home icon or the answer icon when you press, it activates those functions. If it's in the blank area directly to the left of the circle, it activates the left button press. Same goes for the other side.