For the past few months, I've been having issues with my iPhone 4. Whenever mobile data is enabled, the phone heats up and stays extremely hot. It'll stay hot until it runs out of battery (which is usually in under an hour, if I'm actively using data). I haven't updated any software or changed anything recently. At the moment, I'm turning off mobile data whenever I'm not using it, which is pretty annoying. Anyone have any ideas what I should do?