There's been hints of a Windows Phone 7.8 update looming for the AT&T-spec Lumia 900, but little sign of a real timetable. As it turns out, owners hoping to move beyond 7.5 might be satisfied very quickly. Engadget has obtained an AT&T memo that claims the upgrade is rolling out on January 30th -- as in, tomorrow. We don't see any tweaks mentioned beyond what Microsoft itself said last year, although any update would most likely include
