Never had a problem with running out of 3G data on my iphone (1G limit).

Since I upgraded to IOS 6, it’s used up the 3G data limit within a couple of days, 2 months in a row. No idea why. I’ve turned 3G off for now but has anyone else had this issue? I’ve tried one 3G monitoring app but it was pointless, told me nothing.

Read something about iCloud syncing possibly causing high data usage in iOS6

I haven’t had problems personally, but have heard of a few people that have.
There are settings to only sync iCloud when on Wifi.

Make sure that’s enabled first.

aah, just found this.
http://www.guardian.co.uk/technology/2012/oct/17/iphone-5-iphone

Turned all that stuff off now.