If you have an unlimited data plan, AT&T can and will throttle you to unusable speeds if you exceed 5 GB in a single month.
AT&T Acknowledges Throttling Unlimited Users : Read more
AT&T Acknowledges Throttling Unlimited Users : Read more
In your opinion. In the opinion of my lawyer boss's friend, who is also a lawyer who specializes in cases like this, you are splitting hairs.Unlimited =/= unthrottled.
Now if it says somewhere in the ToS that they will NOT THROTTLE users, then you have a case.