Not surprisingly, I've gotten the same answer from the local ATT store as well as from the Premier ATT customer service line. Crickets. Everybody agrees that it is odd, but nobody even has a suggestion (beyond turning "multitasking" items off). One helpful service rep went so far as to tell me that there are many data items that only use cellular even if I'm on Wifi - like email and sending pictures.
yeah well... except that all that works on Wifi with cellular OFF! Ug.
We've had cellular off now for three days, and everything we use on the phone still works perfectly when in wifi range. And there are no more cellular charges. We just can't use the locator services... or actually use the cellular data when we *want* to use it. I'm afraid to turn it back on!
Ah, one thing I found that doesn't seem to work any other way but cellular data is retrieving voicemail... or at least being alerted to same. I turned on cellular data just now for ten seconds. Long enough for the voice mail alert to blip in. Unless that was a big coincidence, I guess there is yet another compelling reason to leave cellular data on.