I have a 3G iPad. I have a wifi network at home and at work and don't need to use 3G at those two places were I spend most of my time. I need 3G only when traveling. Question is: does the iPad choose wifi over 3G when both the options are available? I don't want to use 3G unnecessarily and run up huge bills when I have the wifi option available most times. Any help will be appreciated.