Can iPhone 6s t-mobile option be used abroad US?

I want to use the new iphone 6s in Romania, on Orange Carrier. On Apple.com there is no sim-free option for this iphone 6s.

IF I buy iPhone 6s T-Mobile option (model A1688) from apple store (NOT FROM T-Mobile) paid in full, contract-free, could it be used in Romania? How? What steps do I have to follow? For example, before buying, can the agent from apple store activate iphone 6s t-mobile option for the first time using my romanian Orange SIM, and to see if it works or not?

ANother question would be: is this iphone 6s t-mobile option locked on t-mobile carrier from US? Apple claims that "they do not sell locked iPhones on any carrier". What does this exactly means as long as for now you can only buy/pre-order iPhone 6s with different carrier option (Verizon, Sprint, AT&T and T-Mobile)? What does literally this "carrier option" means?

I Spent many hours trying to find the answer but without succes. I called Apple and they suggested to ask T -Mobile if iPhone 6s T-mobile option will work on a different carrier. When I called T-Mobile, they suggested to ask Apple if I want to buy iPhone from Apple store. Also they said that if a I want to buy this iPhone directly from t-mobile, then the Iphone 6s will come locked and can be used only with a US T-Mobile SIM.

Also I contacted different agents on Apple chat, explained my request. Some of them said that iphone 6s t-mobile option purchased from apple store "may or may not" work on the specified romanian carrer, others said that "will definitively not work" and others said "ask t-mobile and your romanian Orange carrier".

IF anyone know the correct answer, I kindly ask him to provide it here.

PS: last year was the same problem with iPhone6 T-Mobile option. Some guys said that they could use with no problem this type of iphone in their country, while others could not.

THank you