Iphone 5s locked or unlcoked?

I'm thinking about going to the apple store and buying the iphone 5s, but i have a question, how am i going to activate it with my service? I have t mobile. Am i going to have to go to t mobile so they can lock it there or they can do it in the apple store? Or is it already done you just have to ask for it?

You go to Apple Store and buy an unlocked iPhone 5S and you'll be able to use it on any GSM carrier of your choice. It's future-proof. It will also have more resale value. If you need iPhone 5S factory unlocked cheaper than retail, mail me.