Going with the previous post, you could also use the data from the accelerometer to stop vibrate and lower the ringing volume when the proximity sensor goes from covered (in pocket) to uncovered (out of pocket) and the accelerometer hits certain values, as it would mean the device has been picked up, then when the proximity sensor is covered again, answer the call.

Shake to answer might also be nice, requiring 3 specific values to be hit by the accelerometer and the call is answered.