Sudden x10 increase in iPhone data use

Question

I’ve got an iPhone 4, with O2 in the UK.  I normally use about 300MB per month.  That’s suddenly gone through the roof; this month I’ve used 950MB in 2 ½ weeks, including 450 MB in 3 days.  That’s a rise from about 10MB a day to about 120MB.  My phone has received 10MB of data in the last 2 hours while apparently doing nothing.
There’s no obvious reason for this.  I’ve closed down all my apps,  deleted an app I’d recently downloaded (flightrader24), reset my network settings, turned-off most location services, don’t use facebook, don’t send diagnostics info, have deleted my iCloud account and upgraded to iOS 6.  It’s a bit better, but still at least double what it was before.
Any suggestions?
Jedzi

Answer 1

Something sending 4.1GB of data would do this.
I know that sounds sarcastic, but it's true. The phone itself won't decide to randomly send data for no reason at all.
You said you sent photos. Any chance you send a video? That would do it. Any chance something got stuck in your outbox and was resent many times? That might do it.
Basically, you'll have to try and figure out what you did. Most likely it was uploading or emailing a large file, and the most likely large file would have been a video.