There are stories aplenty about iPhone applications raking in big money for their developers, and now it seems MobilityWare's free version of its game Word Warp is joining the rich App Store ranks.

Only this one isn't bringing in the money from game sales, but advertising revenue. The free version is supported by the ad system from Greystripe, and marketing director Dave Yonamine tells TheAppleBlog that, "I find it humorous that people say the ad-support model is flawed."

Having been on the App Store for almost a year, apparently only around 20 per cent of users have opted for the paid version, while around 1.5 million downloads of the free, ad supported game have been made. This figure brings in a secondary revenue stream from the free application of around $10,000 per month, according to the developer.

Calculated since September 2008, that works out as an eCPM (effective cost per thousand impressions) rate of $1.91.

"We’re going to give consumers that choice," Yonamine concludes. "And whatever they go with is fine with us."