T-Mobile set to offer two MiFi routers within the first half of 2011
21Mbps and it will be branded a "4G router". However, no information about the two devices' manufacturer(s) and prices is available, let alone any indication about what kind of data plans the fourth-largest US carrier will offer.
As for the bigger MiFi picture in the US - Verizon and Sprint already have MiFi devices (for over a year, actually) and one more for each CDMA carrier is coming as well (namely, Sprint's Novatel 4082 and Verizon's Samsung SCH-LC 11). AT&T only recently launched its first MiFi hotspot, which offers faster speeds than its rivals and an own OS, but also more expensive service plans.
source: T-Mo News