WeChat registration was a fascinating experience. You download the app and then someone who is already in the system has to verify you via QR code scan. That's how it was when I visited a couple years ago, at least.
Not necessarily "China phone number". I live in Malaysia and WeChat is very popular here, even among Malays. One Malaysian friend vouched for my account.
It works pretty reliable with discoverbank cards, but that's because they are unionpay compatible. It was a complete mess getting the app to the point where it would let me use it for payments at all, though.