On the subject of "tapping phones". I had the idea that you could generate a nice pairing key by using the aligned inertial measurements to validate identity over a public channel (like some wireless protocol). Think of it like Bump 2.0. You could then share contact information, messages, whatever...

In practice it might be a little bit more than a instantaneous bump, and more of a quick shake. Like a handshake, but with phones. Weird, but kinda cool... maybe.