Angry Birds, the insanely popular and addictive game for mobile phones, is expecting to earn more than $1 million a month from in-game advertising on the free Android version by the end of the year. That's almost as much as the company's earning from the paid version on iPhone.

That claim comes from the company's Peter Vesterbacka, whose official title is Mighty Eagle, who talked to TechCrunch earlier today.

Angry Birds costs $0.99 on the iPhone App Store. Between August and November, that version sold 3.5 million copies. That amounts to about $1.2 million per month. So by the end of the year, developer Rovio will be earning almost as much from advertising on Android as it's earning from the paid app on iPhone.

Unsurprisingly, the free app is moving much faster: Angry Birds for Android was downloaded 7 million copies in the month after launch.

This is great news for the Android platform and for developers interested in capitalizing on it. Free ad-supported apps really can make money if you sell enough of them.