We’ve known this was coming for some time, but the light finally turned green for in-app billing in the Android Market.

In-app billing has been a very successful model on iOS and is likely to entice some new blood to branch out to Android. Most commonly developers using this functionality make their apps available for free and then charge for upgrades, virtual goods or additional levels after users have gotten a taste of the app.

When used properly this can extend the life of an app or game and keep it interesting or useful, but when abused it can feel like you are being nickel and dimed to just play the game or use the app as it should have been originally designed.

The initial class of apps launching with in-app billing include; Comics, Deer Hunter Challenge HD, Dungeon Defenders: FW Deluxe, Gun Bros, Tap Tap Revenge, and World Series of Poker Hold’em Legend.

If you’re a curious developer you can find the instructions on implementing in-app billing right here.

As a user or developer what kind of implementations are you hoping to see or place in your apps?