Would an different AT&T micro SIM card work on a AT&T locked iPhone 4S?

I believe the answer is yes but I want to be sure before I sell my iPhone. I don't want to sell it to someone who believes this to be possible and then learn it's not.

I know the phone will not work with any other carrier but AT&T.

If the phone is locked only the sim it's locked to will work.

Yes since they are both through the same carrier.

Any AT&T SIM will work with an AT&T locked phone.