Ringz for Android allows you to purchase extras from within the aplication itself
This is just an example of a feature that´s not natively supported by Android, but the developer has found a way to build it into their application. Aside from Ringz, you can also find several other programs with the same functionality at Android Market – Oracle, Locale, Open Home. Android definitely gives developers the opportunity to be creative and fix functionality gaps in the operating system.
By the way, take a look at Ringz, because the game is quite a brain-teaser indeed.