T-Mobile will launch its 4G LTE network in seven markets beginning March 26th, according to a newly leaked internal document. The first cities and regions to see lightning-fast LTE data speeds from the fourth largest carrier in the nation include: Las Vegas, Nevada; San Jose, California; Phoenix, Arizona; Kansas City, Missouri; Houston, Texas; Baltimore, Maryland; and Washington DC. With Verizon, AT&T and Sprint all having a lengthy head-start of varying degrees, T-Mobile will need to put in a lot of work to close the gap over the next couple of years. Expect an official announcement from T-Mobile by Tuesday, Mach 26.