Data Charges from AT&T while on WIFI??

When your phone goes into standby, the WiFi radio is turned off to conserve battery power and it will revert to the cellular data network. This is normal. The only way to avoid this is to turn off cellular data in settings or leave the phone connected to a power source.

Your phone is in standby if the screen is black. Unless you're connected to a power source, WiFi will turn off. You can set the phone to never enter standby mode, but you better be connected to a power source if you do, as you'll be measuring battery life in minutes. There is no reason to ever turn WiFi off, as any battery savings are minimal & it automatically turns off in sleep mode anyway(unless connected to a power source).

WiFi uses less power when actively transmitting and receiving data than 3G does, but the 3G connection is not actively sending and receiving data constantly. The power useage stats are for an active connection, not a passive one. By its very nature, WiFi is a constantly active connection as it has to maintain connectivity with the hotspot.

My husband just found out that he has overages this month. He rarely uses his iPhone for surfing unless he's at home and even then hardly at all, as he has an iPad. So it was a huge surprise to us to get this email alerts. I see from the others who have answered you that when the phone is asleep, that WiFi is off. That's news to me. I have never heard any one else warn us of that. One thing that was puzzling us, was the timing of these charges - every night/morning shortly after midnight there would be charges - and we definitely knew that we did not do any downloading, or surfing at that time. Not exactly the same time, but all within 15 - 20 minutes after midnight. I was wondering if this has something to do with iCloud - does something back up, sync at that time?

Geraldine

The times reflected on the statement do not necessarily reflect when the data was actually used. It's reported by from the outlying equipment to the central offic in batches.

Take a look at the bill and compare it to the last one. Don't worry about the times for data use, just look at how much data was used a day. Are there any spickes on the current months bill or is every day consistently higher?

I've read that when the device is in sleep mode, it cuts out of wifi mode. But any notifications or other data transfers then go through you cell data plan.