iPhone "contract free" will be unlocked intl' (outside USA) ?

Hi all,

I plan to visit USA next month. I saw tha the only way to purchase an iPhone 6 without contract in USA will be T-Mobile. If I purchase an iPhone 6 in the Apple Store in  USA paying full price "contract free", it will work as "unlocked",  specially in Spain ?  It will be a pleasure to work with T-Mobile in Spain but ....no service!

Thanks