i asked about this twice on apple support chat, they told me well one did no, and the other said ask your service provider because contract free is not the same thing as unlocked. :-/
I can confirm 100% the tmobile one is unlocked, providing you purchase it from Apple's website, which I did. I have both AT&T and Tmobile service and both sim cards work flawlessly.
im so confused though ive read several different articles and website forums saying you can use any sim in it, verizon sim though i get mixed results well im looking.