Major League Baseball has announced that the Passbook app on the iPhone will now be accepted at 13 Major League Parks this year. You can read more about passbook and MLB's forays in mobile and tech in Erica Ogg's article over at GigaOm .
If you are a baseball fan, you might also want to check out her other article about the expanded features of the MLB at bat 2013 app for iPhone and iPad. The app is free, but if you want more than just scores, it will set you back $19.99 for the season subscription. I have had the app installed over the last few summers and it is great. Live audio for all games (from either team), video highlights, pitch by pitch coverage, stats, and more. You can read more about the app at MLB's website.