AT &T MYstery Data Usage

I read this article in the Macworld Best of Best about smart phones and I Phone. AT&T claims. Many smart phone and I phone are always on data devices. They  establish a data connection with our network and keep it open even if their is no data being  transmitted. If you do not end the daily session, it is recorded during a nightly feed to the billing system. THe data session can contain billing for all the data that was transmited throught out the day. When your phone goes to sleep, its wi-fi connection is typically terminated, but the 3G connection remains active.If information is transmitted over the internet while the iphone is asleep, that data will go over 3G even if you have an active wi-fi network that the  iphoine would use in its waking state. So at nght to prervent further  excessive usage. On your phone, go to Setting-General-Network, and turn off Cellular Data.