http://www.bgr.com/2011/03/18/att-cracks-down-on-tethering-cheaters/ Just read this over at BGR. I rarely tether but it's useful when you are in a jam and I've never used over 1.5GB total data each month. I have the $30 grandfathered unlimited data plan. I just wished ATT was fairer in their tethering policy like offering us $30 for 5GB data (total phone and tethering). But their warning to get you to the $45 "data pro 4GB plan" scares me and they warn you will lose your unlimited grandfathered data plan.