Specifically, the TOS state "plans(unless specifically designated for tethering usage) cannot be used for any applications that tether the device (through use of, including without limitation, connection kits, other phone/PDA-to computer accessories, Bluetooth or any other wireless technology) to Personal Computers (including without limitation, laptops), or other equipment for any purpose."
There doesn't seem to be any indication that this policy will be changing. More likely this is intended as a way to make sure people tethering their iPhones are paying for the extra data plan. It can already be done on a jailbroken iPhone, a method that doesn't give AT&T any ability to control whether the user has purchased the extra data option.