In the past two days, as far as I can tell, my wife's iPhone has used 3.5 GB of data. She doesn't stream, download, use Siri. She basically e-mails. She's even on wifi at home and work. Any suggestions on what to do to investigate this? I don't want to be paying $10 a day on this. I've closed all the apps, reset (and it still went through 700mb in several hours since that).