First of all, this is NOT about the huge data drainage others users experience with their iPhone or due to AT&T. I searched for answers everywhere but I couldn't find any. Oh and by the way, my native language is not English so apologize me for any mistakes. After using my iPhone for a few months, suddenly the battery began to drain very rapidly (from 100% to 0% in 8 hours without ANY usage). However this happened just a week before iOS 5.1 was being released, and everything went to normal when I installed 5.1 Now, approximately a month later, all of a sudden, the problem is back again! Started from the moment I synced my iPhone through Wifi with my iMac (used the 'Synchronize'-button in iTunes). Searching for the cause, I noticed (thanks to a data-monitoring app from my carrier) my iPhone continuously connects to their cellular networks. Every 1 to 5 minutes it connects and consumes +/- 7 KBs of data (can be 25KB tops when the last connection was a little longer ago). Ok so I found out why the battery was being drained, now I just need to solve this problem. Then I found something about the Wifi Sync which could drain data for searching the computer again. I thought: "That's it!" since it started from the moment I synced again by Wifi. BUT... turning Wifi sync off didn't solved it! What's even more bizarre: My iPhone is connected to a Wifi-network, but drains data using the cellular network! Why does it uses Edge when it can use the Wifi-network? And more importantly: WHAT is it doing anyway?? What I've tried: Turned all apps off (bring up menu and pressed red circle with minus) Turning Siri off Turning Wifi Sync off Set DNS for the Wifi network to 188.8.131.52 A full restore of the iPhone, but restored it using a backup A full restore of the iPhone, as a new phone (no backup) None of this helped. A full restore helped, but the problem returned not much later. Some preferences I've set: Bluetooth off "Diagnostics & Usage" to "Don't send" Email set to retrieve 'manual' (not push, not fetch) iCloud on, but "Use Cellular Data" is turned off "Use Cellular Data" for the App Store is turned off Home Sharing is turned off Wifi Sync on (turning off didn't solve the problem, see above) Siri on (turning off didn't solve the problem, see above) "Location Services" only on for "Compass calibration" and some apps It must be software-related, since the problem wasn't always there (Had it 3 months before it happened for the first time) and went away with iOS 5.1. Now it however returned after a sync executed from my iMac.