Ever since I switched over to the iPhone, my AT&T "Data Usage" page online has been filled(couple hundred in the past 3 days) with:
To: phone
Type: Internet/MEdia Net
Direction: Sent
MSG/KB/MIN: 2KB-13494KB
It's happens whether or not I'm using the phone, and most of the time I'm on WiFi so nothing should really be sent over the AT&T network.
If you have your location on, it will continually to send info, usually for E911 info if needed. At least that is what I have been told from more than one carrier.