If you're qualified to work for a team that's hiring, transfers are pretty easy. I work for GOOG outside CA and know a lot of coworkers who transferred teams within the company from out of state. Lateral mobility is something of a perk.
Pay depends enormously on the local market for your skills. NYC and Boston pay almost as much as Mountain View, while (ex) London pays much less. People moving between offices are often offered large increases/decreases. A strategy of joining in Mountain View and then transferring to a lower-paying office isn't generally going to give you much higher pay at the new office (though you'll of course have the money you put away while in Mountain View).
(Speaking only for myself)