For iPhone 3G and 3G S users who enjoy their Apps, the In-App Purchase is ideal. It allows extra enhancements to be unlocked within any given App. For example, extra weapons in a game, unlock new songs or levels and so on.
Previously, this feature was only available to paid Apps. Now the option has been expanded to free Apps, according to the Daring Fireball website, which will save developers of free Apps having to produce a separate Lite and Full version of their App.
Apple added that, "In App Purchase is being rapidly adopted by developers in their paid apps. Now you can use In App Purchase in your free apps to sell content, subscriptions, and digital services. You can also simplify your development by creating a single version of your app that uses In App Purchase to unlock additional functionality, eliminating the need to create Lite versions of your app. Using In App Purchase in your app can also help combat some of the problems of software piracy by allowing you to verify In App Purchases."
Click to read the Daring Fireball story