If you’re planning to upgrade your iPhone, iPhone 3G, or iPhone 3GS to the iPhone 4, and want to take advantage of AT&T’s new, cheaper limited data plans, here’s a tip: don’t use your iPhone 4 for a day or three before checking the “Usage” meter that shows you how much cellular data you’ve consumed. (Settings > Usage > Cellular Network Data) A good pointer as of now: start your iPhone 4 fresh rather than…
