Phone came damaged

Likely you’ll have to take it to Apple for warranty service, if it came that way fresh out of the box.

No you do not contact Apple and no this is not a warranty issue. You have to contact AT&T right away. 
This is a customer populated forum not AT&T customer support. It is highly unlikely you will get a response from a customer service representative through this forum over a long holiday weekend. Please call AT&T immediately.

Hi - I am having the same issue.  My iPhone 12 Pro was delivered and when I opened and got ready to activate there is a small nick or hair line crack in the screen.  I have been told a number of things - After my first call to support they sent me to a store - at the store they couldn't help and had me call support while in the store - after speaking with a few reps on the phone a lady told me I had 7 days to return/exchange for any reason.  But now I am looking for instructions on to initiate that process and can't find info.  

Please keep me informed on your process and I will post back here on my process - hopefully we can help each other!  

Happy Thanksgiving!

My meaning is that it’s unlikely that AT&T will want to deal with it.  Assuming that the box it came in isn’t damaged, they will either say that you dropped it and broke it when taking it out, or they will say that it came damaged from the manufacturer, so you need to deal with them under the warranty.  In the end they will probably tell you to take it to Apple, right or wrong.

I totally agree with @dwill05

It's Apple's quality control problem.  But with a brand new phone, AT&T can and should replace it, and deal with Apple themselves. It's just good customer service.