Absolute beginner question- Send buttons to phone (Have some coding knowledge)

How would you do something like this where you click a button and it sends the button to your phone with Arduino? http://www.youtube.com/watch?v=5tCEXEuICWs Also how would the phone read it?

I was thinking about learning how to do stuff with an Arduino board and this really made me want to.

I do have some C++ programming knowledge.

check out the adk - accessory development kit for android. doing this on iphone may be very difficult without jailbreaking / seriously hacking your phone, unless you are posting to a webpage, and just looking at a webpage through your phone. other mobile phones...who knows??