From Ngmoco to Tapulous, in-app iPhone purchases are becoming popular among developers and users.

Apple has only allowed in-app purchases for free applications for a month, but developers are already using their creativity to make in-app purchases a viable business model. 

The Business Insider reports that Ngmoco, famous for their Rolando game, has released another game for free called Eliminate. This game is an online first person shooter that lets you play if you have enough energy. You gain energy by either waiting an hour, or by purchasing "power cells" via the in-app purchase system. 

TBI conducted an interview with Neil Young from Ngmoco, and while he wouldn't tell the revenue from their games, he did make reference to a possible goal of "5 cents in revenue per day, per active user." That's a substantial amount of revenue considering Eliminate is currently the 7th highest grossing application in the App Store. 

All of this goes to show that in-app purchasing could be the way of the future for iPhone development, and it could definitely solve the problems that comes with releasing both a trial and full version of an application. A developer could release one version that could have an expansion pack purchased using the in-app system. 

You can read the full story on The Business Insider.