Android Developers has announced the launch of in-app billing for developers and app users on the Android ecosystem.
What this system does is allows developers to create apps that utilize in-app purchases. In turn, when users are using those apps, they can choose to pay and upgrade or add new features as they are released.
This also opens up an alternative way to try before you by apps in that you can offer a cut down app to users and then when they pay, the extra functions are added on.
A few requirements and help documents have been created such as the need for security and details on how you can test in app purchasing (if you are a developer).
Full details can be found over on the Android Developers blog.