Will a Sprint iPhone 6S purchased in full work with Verizon?

[uhslax24]

So sorry if this is a duplicate. I did a quick search but couldn't find a definitive answer.

I'm looking at picking up a Sprint iPhone I reserved this evening at my local store and buying it as part of Apple's upgrade plan. Will I have trouble unlocking it? Do I need a sprint account if I am not financing it through Sprint?

Alternatively, could I purchase it in cash (no financing) to get it unlocked?

Thanks!