I've been on top of this due to the fact I'm one of those customer who got it from T-Mobile expecting to have it INTERNATIONALLY sim unlocked since day one. Unfortunately after getting in contact with T-Mobile last weekend (i was out of the US) and getting to know the terms&conditions (40 days of active service, more than $50 on refills, etc etc) of course my next question was the same as you...
"So... If i get it from Apple (website/physical store) would it work?"
Unfortunately not. I called like 5 times, I was chatting with reps everysingle time i had time from work (I'm sorry apple guys!) bur the answer it's always... They are both the same iPhone 5s, same model, same carrier, same conditions (either from Apple or T-Mobile store)
In case you want to get an iPhone 5s internationally unlocked since day 1... You'll need to wait for the GSM unlocked version as iPhone 4s and iPhone 5c (already available at apple online store).