If these are anything like last years model, probably not. Unless you specifically choose the sim free model you’ll get one designed for your carrier (ATT) the only difference is it won’t grab the locked policy upon activation.
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Well look at that. Finally one model across the board.
Edit: maybe not. Notice that the iPhone Xs/ Max show A1921, but one for gsm and one for cdma.
https://www.apple.com/iphone/LTE/#iphone-xs