Switching wireless carriers

[The1Metallian]

I'm sorry if this question is dumb, but - when you switch carriers, do you have to or can you reflash your phone to your new carriers' version of Android? More specifically - I'm on AT&T; if I switch to T-mobile, do I get the phone reflashed to T-mobile's skin? I have a Samsung Galaxy Note 4 and it's still on 5.1.1 because AT&T won't update it, but T-mobile has already released Marshmallow for my model. I'm desperate for WiFi calling, apparently only available on Marshmallow.

 

[Almeuit]

You can just pop your SIM into your AT&T phone and it will work -- just ensure it is unlocked.