Because 3G is a power hog; it cuts your iPhone’ battery life in half. Therefore, be grateful that the iPhone even has an on/off switch for its 3G radio; that’s a luxury most 3G phone owners don’t have. You might consider turning off 3G when, for example, you’re not in a 3G area anyway, or you’re not using the Internet. You could turn it off when you have a long work day ahead of you, and you can’t risk running out of juice halfway through the day. Or maybe you’re getting the “20% battery left” warning, and you’re many hours away from a chance to recharge. Turning off 3G forces the iPhone to use the older, less congested AT&T network, which sometimes means you can complete a call in a crowded place where a 3G attempt would fail. In those situations, from the Home screen, tap SettingsÆGeneralÆNetwork; where it says Enable 3G, tap to turn it Off. Now, if you want to get online, your phone will use only WiFi and the slow EDGE network.
Airplane Mode and WiFi Off Mode To save even more battery power, you can turn off all three of the iPhone’s network connections in one fell swoop. You can also turn off WiFi alone.
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