Trouble with this is the carriers won't be able to run national ads with their pricing. Instead the price will have to be concealed until you're about to sign up. Some states (Nevada) you pay around 7%, whereas others (I think NY?) it's 25%. I'm still trying to figure out why the government finds it necessary to make a cell phone so expensive to have, even if your income is shit.
They could still run nationwide ads with the net price but quote the correct amount before you sign up.