By almost every reasonable measurement, Google’s Android OS is giving Apple a reason to check the rear-view mirror. But for many developers, developing for Android is still somewhat unattractive because the common wisdom is that successful Android apps are likely to generate far less revenue than successful iPhone/iPad apps.

One of the possible reasons: paid Android apps are sold through Google Checkout, which Android critics argue offers a far less pleasant experience than the App Store purchasing experience offers iPhone and iPad owners.

But can third parties change that? Two mobile payment providers, Boku and Zong, announced new offerings yesterday that give Android developers the ability to build payment functionality into their Android apps.

With their new SDK’s, Boku and Zong are trying to tap into a potentially lucrative market that doesn’t exist now: Android in-app purchases. Apple supports in-app purchasing for iPhone/iPad apps, but Android developers are pretty much out of luck. Yet for developers looking to monetize certain kinds of free apps, such as games, in-app purchasing can be extremely effective model. And for Android developers who aren’t confident in Google Checkout, in-app purchasing may offer an alternative way to bill for premium content and functionality.

There may, however, be a catch: a layman’s reading of Google’s Android Market Developer Distribution Agreement seems to indicate that in-app purchasing is forbidden (as does this). If this reading is accurate, Google may not be pleased with Boku and Zong, or with developers who use their new SDKs.

The good news, of course, is that the move by third parties to give Android developers a greater opportunity to monetize their apps is likely to force Google to build its own official solution for in-app purchases. And hopefully Google when Google builds this, it won’t forget about user experience. If it can make it easier for users to buy apps (and content and functionality within apps), the burgeoning Android ecosystem will be stronger for it.