So, I was just testing Find My iPhone out on Me.com to see if it could find my iPhone 4. I have the accounts set up and I can verify that it works if my 3G data is on. But, it does not work at ALL if 3G data is turned off, even though both Wifi and cellular calling/text messaging are on. It can't find it at all: no location, no pop up message, nothing. Me.com says it can't find it. This is freaking useless. All someone has to do to defeat Find My iPhone is to turn the cellular data off in Settings.