Does this thing have a GSM radio? Wouldn't that be the only reason to want to change a SIM card?
Just LTE which - my understanding anyway - Is an offshoot of GSM and requires one. But Sprint and Verizon have it integrated it into the phone/chipset/cpu or something so its not removable/transferable but I don't think that would be of much use to users on these networks anyway because even if you could remove it you still need CDMA functionality which wouldn't transfer with the SIM anyway, just the LTE portion.
verizon has sim cards. They can even work on hspa if frequencies are supported. Which makes them a great international device. I expectes sprint to have a sim, but hidden inside the phone out of reach, but no. Which sucks for someone like. Still love my phone though.
I'd hazard a guess that one of the biggest highlights here is that the glossy back can be easily removed from the antenna array, meaning 3rd-party replacements would be easy to swap in. Not that it would be that difficult to make a full back piece with the antennas included, but as far as production goes it makes the idea a bit more palatable, perhaps.