NAD is the National Advertising Division of the BBB National Partners program, and is a self-regulatory body intending to curb unfair or misleading advertising.
This case questioned Boost's advertising about Unlimited Data plans,, when their plans offer capped LTE-speed and 2G fallback (at 128kbps).
The advertising mentions not only 'Unlimited Data", but also Unlimited Video Streaming. The easy part of the decision is that the claims of unlimited video streaming are obviously not true, and streaming is impossible at the fallback 2G speeds. But more importantly, NAD's decision says that the Unlimited Data claim itself is misleading, since it misleads potential customers by not making clear that unlimited 2G data will not allow many of the uses a customer might expect from Unlimited Data. NAD found that Boost did clearly, and in useful proximity, indicate that that the Unlimited portion of data was at 2G speeds, but did not make reasonable efforts to explain the severe limitations of 2G data speeds.
Although the NAD decision does indicate what stance they would likely take on similar advertising claims by other telecom providers, it doesn't extend automatically to other companies, and doesn't have the force of law. The NAD requires a payment to consider an issue from the entity (in this case AT&T) who requests a decision.
I'm a fan of plans with unlimited, or even limited, 2G fallback. I hope this decision helps end the trend of calling such plans 'Unlimited Data' plans, but also hope it doesn't discourage providers from offering 2G fallback at all.