My data usage has spiked the last couple months too. Wtf.
Zach I think I figured it out. In the 5 series of iphone all videos posted on facebook automatically play. So once you open facebook all these video's are being downloaded once posted by any of your friends.
Under settings you have to scroll down to facebook than in there you have 3 choices to play videos on, wifi only, or off. I would suggest you turn that off.
Amazing that none of the big carriers are telling people this. Both US and Canadian.