Tmonews has word that three hot' news devices are headed to T-Mobile in the first half of this year. One is the HD2, another is the Garminphone, and the third would be the HTC Espresso. We've seen some slides of the Espresso UI before but haven't heard what type of form factor it'd rock on. According to tmonews, it's looking like the Espresso will be a myTouch 3G successor with a twist, er, slide. Meaning it could either be a myTouch 2 or myTouch Slide with a 'sidekick'-type keyboard or a slider keyboard.
Everything is very vague right now, but they're hearing a May 17th release is possible. But it's so early in the game, that changes aren't just possible, they're likely. We should definitely know more at Mobile World Congress.