WP 8.1 Tap to Pay requires that you obtain a secure SIM from your carrier. It can be done in the US, but carriers are not generally willing to give just anyone the secure SIM. I don't know why that is.
Still, even then, the Tap to Pay in 8.1 is not really worthwhile at this point. Too many steps, and it is easier to pull out a credit/debit card and swipe it.
There is supposed to be coming with Windows 10 for Mobile a new Tap to Pay that is "supposedly" 100% compatible with the way Apple Pay works. The reason we're not hearing about it is because Windows 10 for Mobile isn't out yet, and it may be one of those things that the phones need to hit the market first, then an update will occur to push out that will enable payments.
It is supposed to be a payment system that will no longer require a secure SIM, but it will require either a fingerprint scanner or an Iris scanner on the phone to be able to use it. That means you'll probably need a flagship.