AT&T adds tethering to iPhone, drops unlimited data plan
I'm not in the least bit surprised. AT&T's network is struggling with 3G load as is, there's no way they could continue to support unlimited data plans, especially at the rate that Apple is selling iPads, not that I know how fast the 3G iPad is selling.
http://www.wired.com/gadgetlab/2010/06/att-adds-iphone-tethering-kills-unlimited-data-for-ipad-smartphones/
http://www.wired.com/gadgetlab/2010/06/att-adds-iphone-tethering-kills-unlimited-data-for-ipad-smartphones/