I am a cricket user, so I am wondering how to purchase iPhone X on the release day online? there are Tmobile, ATT, Verizon and Sprint purchases, so do I just pay full price on either carrier?
Looks like you will have to wait until they release the Sim free version. All the ones you mentioned require that you have an account and are adding a new phone or upgrading an existing one.
Edit: The T-Mobile phone is unlocked but can't be used on Verizon or Sprint.