If you just want to "unlock cores" go buy an AMD X3 720. Then when the 4th core is completely unstable, don't complain.
There's really two different worlds here. i3 is going to be a new architecture, based on a 32nm process. So they are NOT taking faulty 32nm quads and turning them into Dual-Cores, since the current quads are 45nm.
However, AMD on the other hand, has the ability to take Phenom II X4's and turn them into Phenom II X3 720s if a core doesn't perform properly. That's why it's "possible" to unlock a 4th core, because it's physically there.
The i3 CPUs will only have 2 physical cores so far as I understand.