I started experiencing this problem last night. I typically use about half a gigabyte per month, but I apparently used about 4 gigabytes while I was sleeping and my iPhone 4 was connected to my home wi-fi. AT&T has said that they will not charge any overage fees, but they won't tell me which web sites are serving me the data. Apparently I have to get a subpoena to find out what my own phone is doing.
I got a few data monitor apps, I rebooted the phone, I removed and reinstalled the Podcasts app, and I turned off the autodownload feature of the podcast app, and I denied it access to the 3G connection. We'll see what happens. So far, data usage is nill, as it should be.
AT&T was, of course, saying that my phone is busted, and that I'm eligible for an upgrade. When I insisted that I need to know who is serving the data so that I can find out if my phone has been compromised, they got very defensive. ***? If they know what's going on, why don't they just tell me what to do?
And, of course, I get the overage warning text messages at 4 am, as if that's going to help. Even worse, the text message informing me of of 90% within quota allowance arrived AFTER a text message warning me of 75% usage of my overage!
This makes me think this is an AT&T issue. Has anyone else eperienced really screwy service with respect to warning texts?