Controlling an Android smartphone with an Arduino via USB

Hi there, I saw a video where someone controlled a smartphone using an Arduino Esplora and I was wondering how that works. Could someone help me? Thanx :D

I was wondering how that works.

Do you have to know how your video camera works in order to take videos and post them on you twit? (Oops, I meant tube).

What part of your phone do you expect to control? Most people reasonably expect to control the Arduino from the phone.

Getting data to and from the phone is the easy part. Using the data on the phone, to make the phone do something, is the hard(er) part.

Could someone help me?

Without (a lot) more details? No.