I don't believe LA will have 4G/WiMax until Fall. If that May 12 launch party in NY is legit, I believe NY will be the first major market to have 4G/WiMax and then slowly it'll build and be available in the other major markets.
A friend of mine made a good point about 4G/WiMax being available in smaller markets first vs. larger markets. If anything goes wrong in those smaller markets, it's easier to focus on the issues in the smaller markets, as supposed to making it available in larger markets first (which would be a nightmare if anything went wrong).
Then, by the time they've figured out the problems/issues (if any), they can put more time, money and energy into making sure the major markets won't have any problems, which will also help marketing (which is crucial in major markets) and sales.