Take your word for it as i know zip about any of it. Just got a mobile the other day and thought i could put a sim card in first, then arrange a plan with my internet provider as guessed that would be the best/cheapest way. Then was told i had to get a sim card from my provider if i wanted a plan from them. Ten days and still haven't called them.
Didn't even know details of what a sim card did .. https://www.canstarblue.com.au/phone/sim-cards/ . Have always only been more interested in what humans are and how we work, than the same about machines.