Q: The iPhone 5 uses Cellular Data over WiFi?

Gamtu, you could keep your phone plugged in at night. If your phone is asleep, it will revert to cellular data unless plugged in. The tech guy guy suggested to me that some functions of the phone use the cellular data if they don't like the quality of the wifi. If there are hiccups in your wifi connection, they can, for example, finish a large download using cellular data. He also hinted that not everything is ceased by turning cellular data off. I have not seen any evidence of that yet. When I turn it off, I see no usage, even overnight.

Thank you for the tip I'll keep it plugged in.

I have a verizon Iphone 5 with this problem. So I talked to verizon level 2 tech support and while they wont admit that this is a widespread problem, they did bump me up to a higher data plan for the month for free, so I am no longer over. So now that I have data again, I changed a butt load of settings that I wasn't even aware of when I first got the phone to see exactly what kills the data most. Here is what I did when I went to settings:

1. settings -->  general ----> cellular ---> and where it says "use cellular data for" turn all that stuff off.
2. settings -->  Icloud and turn everything off. also go into "documents & data" and where it says "use cellular data" turn it off.
3. settings --> mail, contacts, calendar and set fetch new data to 15 min
4. just go into every item in settings and see if it has a use cellular data option and set it to off

This may help some people if thats really the problem. Honestly, if apple or verizon wont at least mention that they're working on this, then I'm going back to Android because even with 4G LTE phones from them, I never even came close to 2gb of data usage.

If you were me, would you buy the iPhone 5 after apple fix this issue? I don't know what I should do. Should I cancel my order? Because I don't know if this will take a long time to fix or not

Tecal, that's great but now you've got a disabled phone when you're not on wifi.  My data explodes when i go out and have to turn cell data back on to do something like check my mail. A couple MB in minutes. Again, my husband checks his and there's only a few KB increase. Hopefully we won't have to deal with this very long, right?

What did you do to get bumped to level 2?

I am not convinced this is just an iPhone 5 issue, and not also an OS 6 issue. I have a 4 and upgraded to 6 (hate the maps) and since then my Wifi drops out for no reason when my Celullar DATA is turned on. When Cellular DATA is turned off, then it stays connected. This did not happen at all when I had OS 5.whatever.

I absolutly regret hitting the upgrade button. And now I cannot go back to see if it is a phone problem, or an OS problem.

I have been using Apple products since the late 80's and without a doubt the single biggest issue I have with Apple is their arrogance that for some reason or other, they know what is better for me than I do.

Ilazykins Believe it or not I actually had to go into the Verizon store and they put me on the phone with tech support. When I told them that I was inside the store they bumped me up to level II real quick. I didn't have that sort of luck when I called from home before.

But to update everyone who followed my post, Data usage is down significantly but I still track data usage while I'm on Wi-Fi in front of my router. I've used 20 MB of data just being home while on wifi. Something isn't right with this phone or iOS 6.

Sorry to repeat but if you can, keep the phone plugged in. Should not drop the wifi to use data if plugged in. I did a factory reset this morning, then a restore of everything except apps and so far, so good, but I am only going by the numbers on the phone's own log. We called VZ again today.

Count me in. Didn't notice until I received an alert from Verizon this morning that I have used half my 6 gig data plan in 8 days

lazykins, u dont understand, it is using data while its awake, not in sleep mode.

You will need to turn off "cellular data" in settings-general, and turn off "use cellular data" in settings-icloud-documents and data.

No, I won't.. because it does nothing.  How do you people not understand that while you are on WiFi, ACTIVELY using the phone, (NOT in sleep), it is using the DATA and NOT the WIFI connection. FFS

Sorry... Wow. So you have Cellular Data turned off and still using cell data?

I'm guessing you've been told to turn everything off that uses cell data, even though you turn cell data off, too. ITunes, iCloud, AppStore, diagnostics, etc.

I read someone's theory that with a hiccuping wifi connection, it will complete a task begun on wifi using cell data. That is just what I heard. I have seen my data log increase a small amount shortly after turning off data but chalked it up to slow reporting.

Yah I apologize, I am not angry at you guys for suggesting ideas to fix it. I have just done every single work around I can think of, and all that was suggested as well.  Nothing seems to work so it is very frustrating.   I guess time to take it to Apple..

Oh, I see. I think most people here having that problem or some version of it have turned off cellular data while connected to wifi to keep it under control until a fix is found. Your issue must be different if doing that has no effect.