Namco Bandai shined some light on how Nintendo DSi enhanced games work with screenshots from Idolm@ster: Dearly Stars. Plug the game into a DSi and you get more menu options.
The screenshot on the left is what you see if you play Idolm@ster: Dearly Stars on a Nintendo DS. On the right you have the Nintendo DSi main menu, which includes the QR code option. The DSi’s camera can be used to read QR codes, which are kind of like barcodes for cell phones. QR codes give idol masters access to extra items. So far, Namco Bandai has not announced any plans for paid downloadable content for Idolm@ster: Dearly Stars. Maybe, they’re making Idolm@ster trading cards with QR codes.