When you buy a new phone from AT&T Wireless, your eSIM or SIM card is set up and activated. However, when you switch to AT&T and bring your existing phone, you must activate your new SIM card ...

If your new phone no longer supports SIM cards, or you don't want to use them anymore, you can convert to eSIM instead.

the nature of the SIM card means compatibility is a given. Indeed there’s every reason to believe that very same card, now 20 years old, could be installed in any number of phones on the market ...