Using Wi-Fi you can setup your iPad, iPod touch, or iPhone as a MIDI device if you have an app installed that utilizes OSC.
This is especially helpful if you want to play the piano but hate the keyboard version in GarageBand and you don’t have the money to go out and buy a MIDI keyboard for a few projects.
The apps will need an OSC server on your Mac. Some apps work with Pure Data, while others work best with OSCulator. Either way, you’ll be controlling GarageBand with your iPad or iPhone from across the room.
If you’re feeling like Wi-Fi just won’t cut it, Line 6 has the MIDI Mobilizer dock accessory.