That's what I thought, too. Until I figured out that Apple's unlocked "Upgrade Plan" iPhones actually do require a post paid plan for activation. Hence my question

I was merely talking about how unlocked phone works. It’s either you pay a post paid plan or not, as long as they say it’s an unlocked phone it will work on any kind of SIM. Apple sells another type of unlocked phone that is not tied to any carrier just like the other guy posted. That’s what you should get so that it won’t require you to activate and pay any kind of post paid plan.