Sim cards aside from trying to reuse them are actually very flexible.
They come in 3 sizes but can be converted just by physically cutting them down to the size that's needed or just using the smallest size and an adapter set.
Prior to verizon switching to LTE all of their devices were CDMA and if you wanted to switch devices you had to call the company and read off the number of your new device to switch them (could also be done online later)
If they didn't recognize your device for any reason it couldn't be used.
Like today it's typically possible to take use a sim from one device in another even though the carrier would never allow you to activate the device they will allow a swapped sim to function in it.
I have personally been affected by the system CDMA used, I had a grandfathered plan and to force me off of it they prohibited me from being able to swap in any other device even of the same model.
Yet I can take a sim from a smartphone with a grandfathered unlimited plan today and use it in almost any other device of my choosing without further permission from verizon.
Soon if not already people will find that verizon will refuse to allow them to activate devices without VoLTE support.
You will still be able to use CDMA devices until the end of 2020 but verizon will refuse to activate them likewise with LTE devices without VoLTE support.
However the devices with LTE but no VoLTE with sim cards can just swap in a card already activated on an approved phone and continue on until the network is shut off.
e-sim brings LTE and 5G back to the cdma days where you have to ask your carrier permission to do anything.
Sure you can activate your device without switching anything out but we had that before and already know where that leads but seem to have forgotten even though the networks haven't even been shut down yet.