said by borka:
Its probably the data that's being generated from the Iphone/iPad talking back to apple, and sending usage statistics and what not.
They did NOT turn the phone off
disabled all push notifications and location services, confirmed that no email account was configured on the phone, closed all applications, and let the phone sit untouched for 10 days.
I am sure that the phone, as long as it is powered on, is communicating to something. Either Apple or AT&T concerning status, automatic backup of contact lists, or something else.
I wonder what their data usage would have been if they just powered off the phone or iPad completely and not just sitting in standby mode where it can still communicate?