From what I read this morning, international version of the One X will be with AT&T. Therefore, the chance of One X being available on T-Mobile dropped, but its not for sure until CTIA in May. Hopefully they'll announce something.
Other than that, T-Mobile customer may be able to use international version of the One X on T-Mobile someday. Since T-Mobile may or may not be refarming their 1900 GSM spectrum. If they do refarm it to 1900 UMTS, then I'll be one happy T-Mobile customer.