I bought a MiFi dongle and a 2GB international data sim to use abroad (to avoid roaming charges). I switched off Mobile/Cellular data, and left the phone connected to the dongle via WiFi. I burnt through 2GB in 4 DAYS!! Usually I don't even use 1GB per month of data. But I realised I'd forgotten to turn off the settings which back up your photos/videos whenever you're connected to WiFi. So any video I took was getting backed up 'over WiFi' (ie eating my data) instantly. Even when I did switch this setting off, and bought another 1GB, I got through it so quick. I couldn't work out where all the data was going. I'm going abroad again soon - please has anyone got a checklist of everything I should turn off to stop my phone using WiFi data as and when it wants? I believe the App Store will force you to download iOS update installers when on WiFi and there's no way round that. Is there anything else that truly can't be switched off?