Math Geek :
in the begining when the iphone first came out, unlimited was unlimited. they realized hey could not support it so they went to data caps. we all know it, and understand how the caps work. so to offer "unlimited high speed data" yet have a data cap is not only dishonest but contrary to everything we now know about how our mobile data works.
Ahem, I've had a data plan since 2000. Long before the iPhone was even a glimmer in Steve's eye. Contrary to what Apple would have you believe, smartphones and cellular data existed long before the iPhone.
When they first advertised data plans, speeds were around 10-30 kbps. 1.5 Mbps DSL was the norm, and cable modems offering 5-8 Mbps were starting to show up. So nobody serious about using the Internet would be satisfied with a cell phone data plan. Not to mention you had to unplug the phone from your computer in order to charge it (first combo data+charger cable I saw was in 2004). So the carriers figured it was safe to advertise them as unlimited. I pointed out at the store that that could become a problem when data speeds got faster, but the sales rep shrugged it off since it wasn't his problem.
When data speeds got fast enough that you could realistically use your phone as your only Internet connection, they first tried to throttle it. That was bad enough on a plan they were selling as "unlimited." But in addition to that,
they didn't tell you what the cap was. You'd be using your phone's data, then suddenly with no warning - blammo, you were at dialup speeds. The cable companies tried this too. For years they'd cancel people's service for exceeding a secret monthly bandwidth limit. Kinda like police giving tickets for exceeding a secret speed limit. I'm not sure what they were thinking - trying to intimidate people into lowering their usage even if they weren't near the cap? The whole thing was just ripe for a FTC investigation.
Now common sense is finally prevailing. Up til now, marketing departments have resisted honest disclosure because they didn't want anything which could be perceived as a negative or a drawback. The companies are finally telling marketing to STFU so they can tell customers up-front what the monthly data cap is, and exactly what happens when you exceed it. AT&T's fine is for not disclosing this throttling to customers on grandfathered unlimited plans.
(As for throttling an "unlimited" account, there's enough wriggle room in the term "unlimited" because even if you saturated it 24/7, you were still limited by the connection's bandwidth. And the actual bandwidth is determined by how much data other customers use. In other words, "unlimited" does not equal "infinite" and is subject to organic bandwidth limits. In particular, AT&T was fined because rather than throttle only if the tower's bandwidth was saturated, they throttled the moment you passed a GB/mo limit even if the tower had plenty of bandwidth available.)