
Where's your source for that?
Apple appears to be following the same policy they have in place for iPhone 4s - if you buy a full price AT&T phone, it is unlocked, just the same as if you get the 'unlocked' SKU. The model number has nothing to do with the IMEI database unlock status.
https://www.macrumors.com/2011/06/27/all-no-commitment-att-iphone-4-purchases-coming-unlocked/
You do need to buy it at an Apple retail store, though, and make sure the sales rep chooses 'Device Only' on their POS handheld. They should not need your phone number or any other AT&T account information if you're doing it right. Any phones sold at an AT&T store are added to the IMEI lock database.
I'm enjoying my unlocked 4S right now