NO SIM CARD

Call Apple. It's their product. Maybe it needs and eSIM?

Not enough information. We can't tell if the iPhone 13 has suddenly said no SIM, or if it is new to you and you have not installed a sim. Please explain better

Are you trying to activate the iPhone 13 and it does not have a physical or an ESIM installed?   Do you have a previous phone with a physical SIM? Have you moved the SIM from an old phone to the iPhone 13?  

Dad has had this phone for a few years. 2 days ago the phone suddenly showed SOS in the top right corner with NO SIM card available. We tried all the resets requested. Toggle on off airplane mode, toggle on off do not disturb. Hard reset ( nothing happened) turned on and off same error. Reset network still shows no SIM card. Took SIM card out and reinstalled. No damage, never dropped, very clean inside SIM slot 

I don’t think it has anything to do with the outage, he’s in Oregon and mom’s phone is working fine 

So either his phone has failed, or the SIM card has failed. Simple test is to swap SIM cards with another AT&T phone and see if the problem follows the SIM card or stays with the phone. If the phone continues to not read a SIM card that works perfectly well in another phone then his phone is faulty and needs to be repaired or replaced.

If the SIM card doesn't work in another phone then the SIM card has failed and needs to be replaced. Cross your fingers and hope that's the problem

It will be a simple fix to go to an AT&T store and get a new SIM card made with his existing phone number, or have his phone number put on the ESIM which exists in the iPhone 13