* The phone needs to unlock the instant the agreement/deal ends. Automatically, without the need to phone home to the carrier to get it done.
* If the phone is on a payment plan, that shouldn't have anything to do with this; it should be unlocked from day one, and if the customer decides to switch carriers, they're still on the hook for paying out the rest of the payment plan, just like any other credit arrangement.
* Carriers must be agnostic to the devices on their network. They should not be permitted to refuse to allow you to bring your own phone, as long as that phone has been certified by whatever relevant regulatory body as being compliant with the various mobile radio standards.
I don't really get why there's so much consternation around this. If people want free or reduced-price things, sometimes they have to give something else in return.
If they don't want to, they can buy a full-price, unlocked phone. As long as that option remains, I don't see the problem with carriers offering alternate terms.
But I still don't get why the carriers are upset. They can still pair a free/subsidized phone with a 1- or 2-year service contract, with early termination fees that recoup their loss on the phone. Sure, having the phone locked is an incentive to either stay or pay the termination fees, but do enough people to matter actually manage to avoid paying the termination fees? Seems unlikely.