Measure the speed of tennis shots with your iPhone! I should be possible to create such an app because the iPhone has a motion sensor. I envision placing the iPhone in a plastic cradle at the end of the court, my tennis partner does the same on his side with his iPhone. Both phones talk to each other and recorded the speed. The speed can then be instantly seen on the iPhone, which beeps, to say it has recorded the speed, and better yet the speed numbers are transferred in larger scale to your iPad which resides on the bench, so both players you can read them from their court location.