I apologize if this is a dumb question showing my lack of knowledge . Looking at an xr directly from the Apple store. My carrier is Verizon but it seems I should buy an unlocked or what they call sim free. I’m confused by that last term. Do the unlocked versions literally not use a SIM card or is it they just don’t come from Apple with an activated sim and I would just use my current Verizon sim in it? If it doesn’t use one how do you get it working?