I did some digging around in an old jailbroken iPhone (iOS 12) to try to figure out how to stop broadcast alerts from the cell towers and there is a database on the device itself with various parameters from cell carriers around the world. So there are least some settings that are “hard-coded” in each OS release which don’t have to be sent from the carrier - the iPhone will do X based on the SIM in the phone or the network it’s roaming on.
Not sure if tethering is one of the parameters , but there were quite a few.
Not sure if tethering is one of the parameters , but there were quite a few.