First month we all got our iPhone 4S's a couple of the girls on the plan got really close to going over their data really quickly. They got close to going over their data because of excessive iMessage usage. iMessage is great for me while at school because reception is terrible there. Seems like there should be a switch that only allows iMessage use while on wifi and does not hog data. Is there just a thing or am I missing the boat? Shortened version: Is there a way to only allow iMessage while on wifi?