Starbucks has made their Card Mobile app available for iPhone and iPod touch users, allowing you to scan a barcode on your device andthe same way it currently works for gift cards. The app works in conjunction with your already existing Starbucks cards. I tend to get a lot of Starbucks gift cards for birthdays and holidays, so it's nice to be able to keep them all in one spot.
You can create a Starbucks account within the app and then add all your cards. You can also add any valid credit card as well to refill your Starbucks cards (or use the Paypal feature on iPhone).