I remember vzw being on 3g and not having Sims. It made changing phones a bit of a hassle. I hated having to either go into a store or call in. Hopefully there's better ways in the future if this does happen.
It was annoying before because there was no sim. You had to register your device with the carrier for it to work. So it always meant a call to your provider to do anything and you couldn't use the device on more then one network.
E-sim is different. You can have multiple esims on one phone and even move them to other phones.