Well you could takee out the sim :P but doing that too much can damage it ..

Have you looked in Settings > Phone to see if you can disable the radio?

I dont have a sim installed yet so i cant open phone in settings.

Also is there a option for it if you click in the battery monitor area at the top of the screen next to the clock ? that is where you can turn on/off the webcam, the wifi, and a few other things.