Your phone may see more than you think (and do).
Pick up a random remote, for instance, point it at your phone's camera — and press the on/off button. If the phone is on, too, and the camera app open, you might see the infrared light from the remote flicker across the screen.
Now, from your phone's somewhat secret abilities (maybe you can send covert messages across the room with them) to adding abilities to your phone with a secret email address (you can send photos across the world with it, of secret messages maybe):
›› Your Facebook account has a secret email address. Keep it a secret, and use it to post to your wall or share media. Here's how to find your secret Facebook upload address, and how to reset it if it gets lost.