When I first got the phone a few days ago, when I turned on Wi-fi and connected, the 3G icon up top went away (I assumed because it was using the wifi for data). Some time today (and I can't think of anything I did that would change this) when I connect to a wifi network, the 3G icon stays put (and even occasionally displays activity). Anybody have any clue why? And can I undo whatever was done? (Does it even matter?)