just go to MLB.com on your browser (in the BB) and pick a game. You have to option to watch the box score or live pitch by pitch. It's not an app, just the website.
Only the new curve can do the MLB At Bat application.
Another service they have is text message updates. During the game, text the name of your team to 65246 (MLBGO) and it will reply with the current score, who's pitching, and who's batting.