iPhone SIM

It’s a little more involved than just “moving the SIM” … but not much more.

Here is a guide:

https://support.apple.com/en-us/HT210216

Interestingly, no.

It really highlights that your iPhone is a computer that - oh by the way - can “also” make phone calls.

The SIM enables the “calling” part … which depending on your location might also be it’s only “data path” …

… but the the device will still generally function even w/o a SIM installed - especially if it has WiFi connectivity.