Is my iPhone model number MC922LL/A unlocked or locked? I have seen that there are many other model numbers of iPhone 4S's, but I have not seen any info about model number MC922ll/A

Is an iPhone 4S of this model unlocked or locked to a specific mobile carrier?
I got a 4S MC922LL as replacement phone from A pple(my 4S was having issues).

I put my friend's T-Mobile sim and it is working.
I've tried it multiple times even after restarting the phone and it is still working with the T-Mobile Sim.

It seems to be unlocked.