iPhone 4S, iOS 6.0, Verizon version 13.0. I discovered almost 500MB of data usage at approximately 2 a.m., while I was asleep. I had downloaded some albums to my computer, and the phone presumably was syncing. However, WiFi was on during that time, and I have both iTunes and the Podcast app set so that "use cellular data" is OFF. Any reason why this might be happening? I tried following the instructions for the iPhone 5 fix (go to Settings - General - About to update to carrier version 13.1), but my phone is not suggesting a carrier update.
Thanks for any thoughts. I'm almost out of data, only 5 days into my plan!