So my understanding is the Sprint iPhone 6 models are the A1524/A1586 models, which have the most number of network bands/frequencies. So in truth, those are the true 'world' iPhones (even more so than the Verizon models). Now the A1524/A1586 are sold unlocked overseas if purchased full price (you can go to the Apple Canada website and see this).
Not that I'd imagine many people would do this... But what prevents someone from buying one of those models overseas, bringing it to the US, giving Sprint their MEID number off the box, and asking them to activate it on their network (even though it wouldn't have the UICC SIM card)? It's a compatible model phone (literally the same phone hardware).
I mean, the iPhone 4 (CDMA model) didn't have a SIM card, and it works on Sprint's network. So I have to question why technically the UICC SIM is 'required' in this case (specifically, activating an overseas-purchased A1524/A1586).
Trying to understand...