The terms of the agreement state that if you don’t use all of the data you’re allotted for a given month, you lose the ability to use it in subsequent months. It’s called informed consent. There is no coercion (specifically, theft) in this situation. It’s not “your data.” If you don’t like this term, renegotiate, do business with another provider, or go without. You don’t have a right to a service except under the terms a provider is willing to provide it to you (not any more than a given provider has a right to your money, except under the terms you’re willing to give it to him – which is precisely why companies compete with each other to make their terms more compatible with your desires).
These are very basic concepts which underlie the free-market, but unfortunately most people in contemporary society are completely clueless about them – and therefore hostile to the free market as such. This cluelessness and hostility is what T-Mobile is exploiting in this commercial. They’re using the public’s widely-held notion that for-profit business activity necessarily involves harming others (in this case, the customers) in order to emotionally manipulate it’s way into a favorable position in the viewer’s mind. Apparently the company’s superior product isn’t superior enough to “sell itself.” Instead of simply distinguishing itself by emphasizing the fact that it offers “roll forward” data plans, apparently T-Mobile it has to also impugn the moral character of it’s competition.
This is the kind of short-term, opportunistic, self-defeating behavior that is paving the way for the complete destruction of the free market (since it is people like this commercial’s viewers who are the ones who elect anti-capitalist politicians). When that happens, T-Mobile will be one of the victims of that destruction, and they will have no one to blame but themselves.