[ajg1977]

Possibly. Until now AT&T have ignored (or been unable to detect) people who had artificially enabled tethering. Now that they have an official tethering plan,if they do have a way to detect unofficial tetherers then they may automatically add tethering to your account. This is similar to what happens if they detect you using a smartphone without a data plan.

[whatusername]

They charge you for just having a phone that can use data? Or they charge you because you are actually using data? If it's the first then it is crazy.