I would love to know where anyone would have a case.
AT&T has clarified the point of throttling... it's when a customer uses more data than 95% of the other customers. Yes, there are questions regarding markets and why some people are being throttled and others aren't, but, if court ordered, it shouldn't be difficult for them to prove that the vast majority of customers use less than 2GB.
As they maintain that they're only throttling the top 5% to better serve the other 95%, they are offering acceptable service. Whether that's true or not is irrelevant as they can easily work up numbers to show whatever they want/ need them to.
They announced the policy changes at the end of last July and said that they would begin throttling in October. That gave anyone who didn't agree to the new terms a couple of months to leave AT&T without an ETF.
The original contract states they can change the terms so long as they give ample warning and a chance for customers to leave without an ETF if they don't agree to the new terms. They did that.
If you repeatedly call and complain, they might still let you out of contract without an ETF otherwise or, if you really want to stay with AT&T, a few people have reported here that they were able to change to the '5GB and tether' plan and receive various other discounts so it remains the same price.
Either way, the days of 'unlimited' data on AT&T are long over. It's time to accept that and move to a tiered plan or move to another carrier.... or downgrade to a non-smartphone where unlimited is still available and, as I can attest, still remain unthrottled regardless of use (I've averaged between 10-50GB on my non-smartphone plan since the throttling began).