The $400 million sale of iPhone video game maker ngmoco to mobile portal DeNA Co. marked the realization of over ten years of investor hopes and software development: the age of mobile software being big business has finally arrived. Apple Inc.‘s (NASDAQ: AAPL) App Store, the Google (NASDAQ: GOOG) Android App Market, Nokia‘s (NYSE: NOK) Ovi Store, and soon Microsoft‘s (NASDAQ: MSFT) app storefront on the Windows Phone 7 operating system are delivering on the promise that mobile software makers were making for ten years but weren’t realized due to the underdeveloped western mobile phone market and a lack of common operating systems. The age of the app is changing revenue models in more ways than one today. A new study compiled by Flurry, an app company itself that sells an analytics application to be used in conjunction with others on Apple’s iOS platform, shows that in-app micro-transactions generate 9 times the revenue of advertising on Apple’s mobile operating system.

The Flurry study, published yesterday tracked revenue generated by individual users from in-app transactions and advertising on iOS from September 2009 to September 2010. While advertising accounted for the lion’s share of revenue earned on iOS in 2009, a dramatic rise in in-app revenue began in March of 2010. By September 2010, in-app purchases averaged about $9 in revenue per individual user, while advertising fueled purchases averaged just over $1. As Flurry vice president of marketing Peter Farago pointed out in his comments on the study on Flurry’s official homepage, it’s been commonly thought by industry insiders that since the most popular and widely downloaded apps on iOS platforms like the iPhone and iPad are free video game and social networking tools, advertising would be the primary earner for businesses on the platform. Flurry’s data is based on a sampling of unnamed iOS social networking and social gaming apps that the company claims has a reach of 2.2 million daily users. While that test group doesn’t represent the more than 50 million iOS users across Apple’s three mobile platforms, it does reflect common app usage according to recent studies by Nielsen Company.

Flurry’s findings point to one of two futures on iOS. The first is that advertising agencies ramp up their presence on not just iOS, but Android and other competing mobile operating system market places. Now that the market has proven audiences, advertisers may see new opportunity and fertile ground to recapture the advertising markets that have disappeared from print publications and television. This would be especially good news for Apple shareholders anxious for iAd to grow as a competitor to Google in the ad space. The second is where advertising becomes less and less of a factor in generating revenue as micro-transactions become more commonplace outside of social networking and gaming apps. Flurry’s data is compelling, certainly, but the true test will be what those revenue streams look like for the average user in the fall of 2011 rather than 2010. As of this writing, Anthony Agnello did not own a position in any of the stocks named here.