IPhone 4s att change to version?

I own a iPhone 4s I'm using AT&T sim. I want to know if I use version sim Would I have to unlock the the iPhone?

Nope.

All AT&T phone are GSM devices.

A GSM device will not work on Verizon's CDMA network.

Verizon is a CDMA carrier meaning no sims cards so you can only use CDMA phones on their network for example (sprint) so you would have to buy a completely new one

Of Course No, This is Look Like Similiar Problem Like gevey sim unlock, iPhone is GSM Version, So You can't Unlock it, Even if you Know About it.