is “Apple iPhone Payments” available to select during preorder when new iPhones are announced for sale?

I saw a new payment method while helping a friend purchase a phone through the Apple Store app called “Apple iPhone Payments” I would have liked using this option better than paying in full when I was purchasing an iPhone myself a year ago but did not know this was a thing. Am I correct to assume this is basically a watered down version of the iPhone Upgrade Program as in no AppleCare+ included or option for yearly upgrade? And if this Apple iPhone Payments option IS available during the night pre orders go live next iPhone release are all iPhones purchased through this option unlocked out of the box if needed? I travel out of the US and find unlocked phones useful for this...this is an example of what I’m speaking of, when the next iPhones come out next month would I be able to preorder using this option and would I be able to switch carriers at any time without worry of the iPhone being locked to the carrier I select first?