Each phone has a unique identifier called its IMEI, communicated to the network while the phone is connected. IMEI numbers are allocated to manufacturers in clearly identifiable blocks, and so the network always knows what model of phone is connected.

It's not in the SIM, it's in the phone.

Among other things, the IMEI allows networks to block access by phones reported as stolen, even if the thief (or duped buyer) changes the SIM.