Do their unlocked phones really work on non-approved carriers? I never really looked in to it, it's pretty cost-prohibitive. Also, that doesn't help people that want to buy used last-gen and save a few hundred bucks, or the people who are now off-contract and are still happy with their phone but looking to move.

> Do their unlocked phones really work on non-approved carriers?

yes, obviously. 'unlocked' = 'works on any carrier with which the technology (ie GSM/UMTS, works on the right bands) is compatible'. note that since tmobile almost exclusively uses an unsupported-by-Apple band for 3G (1700MHz), you're getting EDGE at best.