An eSIM (embedded SIM) card does everything a physical SIM card does ... activating an eSIM is the way to go. As long as your phone is new, it likely supports eSIM cards. You'll scan a QR code ...

You can activate your AT&T SIM in-store, online, or by contacting customer service. The process is similar for postpaid and AT&T prepaid customers.

In this way the customer ID (and ... All GSM phones and most iDEN phones require a SIM card to operate. There are certain types of phones (CDMA, TDMA, AMPS) that do not use a SIM.

But a bit of hacking allowed him to add a SIM card slot to it. Even though he’s not the one who originally found this hack (XDA thread here), his write-up is definitely an interesting read.