Import China phones don't usually have the United States CDMA/EVDO bands in them, so it ain't going to work with Verizon or Sprint. Although many of them will work with China Telecom CDMA/EVDO, including the 6X.
Can always check the carrier's BYOD policy to see what will work, but AFAICT it's usually certain Samsungs, HTCs, Motos and iPhones.
This is a useful resource:
willmyphonework.net