Gaucho100K

I have a prepaid AT&T Sim card that I will use in my unlocked Iphone4 while in the states... I use the phone only to make voice calls.... but want to avoid having the phone automatically download emails and do other data things... not sure how I need to change the settings to do this and if I can set the phone to manually disregard all data functions while still remaining a usable cell phone.

Thanks...