ROFL .. you're funny.
On the surface, you're correct, however we don't live in that world you're speaking of bud.
Even under contract, these providers have proven to us all over and over again that the contracts are just so that WE follow them.. they don't have to. They change what ever they want, when they want, and tell us if we don't like it they'll let us go. The last one that tried that was Sprint when they took my unlimited 3G data and put a 5gb cap on it for the same price while I was under contract. A bit of telling them that wasn't going to happen, well, to this day I'm still unlimited on my 3G data. I'm no longer under contract and they CAN pull that away from me, but since 2008 they have not.
OUTSIDE of a contract, still, no, they can't just do what ever they want, per-say. There are still certain rules they have to follow set by states and fed and have to abide by those. But in theory, yes, they have more flexibility to change things at will. MOST the time they won't do that because they do realize you can leave. A sheep (customer) out of contract is a threat their existence. There still is a little bit of a balance act they have to play when they make changes. Verizon has had the biggest balls as we all know in standing their ground. Who knows if this will ultimately harm them in the long run or not. Having AT&T follow in their in-on-the-game moves, it gave VZ an upper hand to pull the stunt they did. I just feel sorry for all the VZ customers who paid full price for a handset to keep unlimited data who are inevitably about to have that plan pulled as well.
You're absolutely right about grandfathered plans too.. but, in a sense, those grandfathered plans may as well be the same as being in a contract. AT&T knows that as long as people are GF'd, they're less likely to leave so they can keep their plan. They rarely pull plans away like that.. What they will do is give the illusion that something better is out there, get you to switch, etc etc. But grandfathering is actually MORE of a reason to stay with a provider over that of an actual contract. I'll pay the ETF ANY-DAY if a provider pisses me off.. and I have! (I don't see it as a threat.. I see it as I'll either buy the handset outright, or over time.. either way I'm paying that price) But, I'm more likely to stay and keep my "unlimited plan" in this example, because I know that once I leave I won't get it back. see?
These guys aren't stupid.. we are.