From now on carriers are allowed to sell both locked and unlocked phones, but they have to clearly state which is the case, and what are the conditions of the lockdown (e.g. monthly discount, preferential prices). Also, the phone lease contract must be independent from the line contract. And the phone lease contract must provide a way to get the phone unlocked. The typical case will be something like "I give you this phone if you pay $X upfront and $Y monthly for Z months. If you have a voice plan with us, we'll discount you $Y for the first Z months".
I agree that changing previous contracts is somehow abusive against carriers, but IMHO it's the only way to encourage the first big wave of people switching. The market appears to be OK with this so far, and carriers already started aggressive marketing campaigns to steal each others' customers.
(Yes, I live in Chile. Sorry for suboptimal english ;) )