in general, T-Mobile phones are full price but not unlocked. you can call CS afterwards to unlock it, but they require you to use the phone you're getting unlocked for a month, or something like that.
with iPhones it might be different depending on where you buy. in the Apple website, TMo phones are under "unlocked," so obviously it's unlocked if you buy through Apple. it's probably locked if you buy directly through TMo.
since Apple usually doesn't make unlocked phones available for a couple months, no one can say how they'll do it this time, since TMo wasn't an official carrier until after the unlocked 5 came out. my guess is it will be locked to all carriers this time.