Phone interfacing with the mega adk?

Hello everyone,

for quite some time now I've been trying to get my android app to communicate with my arduino mega ADK controller. What the app should do is simple: when I press "ON" on the application a motor should start turning. But I can't figure out how to send the signal (or code). I'm trying with a usb-cable, I know it's possible with bluetooth but that's not really an option.

Does anyone have any ideas or tips?

Thanks in advance