Which version are you getting? The Verizon one? I've read that's an unlocked version?
If you buy outright, the TMobile, AT&T or Verizon are all unlocked. The benefit of getting Verizon though is it’s compatible with all networks—or at least that’s how Apple’s skus have worked until now. If you buy a ‘sim free unlocked’ model from Apple directly as you can right now for the 8/8 Plus, it’s the same model as the Verizon version. Unfortunately, doesn’t look like we’ll be able to preorder sim free models of the X.
I’ll be buying outright, no upgrade plans. I’m aiming for the Verizon version but if the website requires carrier account info to apply to the phone, I’ll be getting TMobile versions as that’s my carrier.