Sprint uses SIM cards but they are tracked by their network and are permanently tied to the phone’s ESID in their database. You cant just swap one to your new Sprint phone and start using it it. Because of that I don’t really see the advantage of using SIMs on their network, as the whole idea of a SIM is to make your cellular account portable between phones. If you have to go to Tech Support to get your phone switched over (and they always mail you a new SIM card) then what’s the point of having them?
Sprint is a legacy CDMA carrier and that’s why their system works that way. They have SIM cards on current phones because most phones today require a SIM to be present as they are multi-network phones and have a SIM tray or use eSIMs - and they require *something* to be present for the phone to initialize.
Forgot to mention - they also have to have a SIM card to access 4G LTE networks, as to connect to 4G LTE, you *must* have a SIM card.
Sprint will reportedly kill access to their network for anything less than 4G LTE in 2020 or 2021, Verizon is killing their 2G and 3G CDMA and forcing LTE at the end of this year.