Not Bitcoins, but you can this new alt coin:
http://www.mangocoinz.com/Works off your phone's accelerometer, so if you run in place, shake it, or move alot, you'll see the coin amount go up.
Thats actually hilarious as a concept. I love it.
Of course, I see absolutely no way that sort of "proof of work" could be secure, but hey, who cares.