T-Mobile has just launched a website that confirms the imminent release of an HSPA+ smartphone. Android Authority reports that this web page contains references to a device named the "Vanguard" at various points in its code.
Odds are, this Vanguard thing is actually the G1 Blaze. It is believed to have a 3.7" screen, 1 GHz processor, and sliding QWERTY keyboard. The Blaze will be marketed as the successor to the G1, T-Mo (and the world's) first Android smartphone. Look for a launch around September 9th.