k so i have my first genarition iphone with its pay as u go sim card, lets say i buy a iphone 3g on ebay since its alredy atcivate and wat would happen if i put my first generation sim card on that iphone 3g? would i be able to use it normally like my first one? and is there any way i could add the 3g date for the pay as u go by calling at&t?