Sorry if posting to a wrong board, have not found one dedicated to billing.
There are five Android appstores that support in-app purchases today (Google Play, Amazon AppStore, Samsung Apps, SK T-Store, NOOK apps). But all of them have their own proprietary APIs for in-app billing. So if you create an app or a game and want to support in-app billing you have to write five different pieces of code for each of them.
We have started an open source project to create OpenIAB library. OpenIAB Lib will wrap appstore in-app purchase APIs of all the stores and provide an easy way for the developers to develop their apps/games in a way that one APK will work in all the stores and automatically use right in-app purchase API under each store.
If you are interested please join us! So far we have just created a sample game that supports in-app billing of four appstores with one APK file.
Project is open source at GitHub: