With discovery one of the main issues for developers operating in Apple's 120,000 app-strong App Store, any option which can get eyeballs on your game is a valuable thing.

Mobile advertising network GreyStripe took an innovative approach to problem with its '99c per iPhone app download' deal in November 2009.

In this, it guaranteed the first 200 companies to sign up to a $10,000 deal to advertise a free app would only pay 99c for every app downloaded, rather than the $2.50 to $10 per download it said rivals effectively charged for each download via their pay per ad click models.

Now the results of the initiative have been announced.

GreyStripe says companies such as Kraft, the world's second largest food company; social gaming company PlayMesh; and envIO, which developed the Chorus app, signed up.

It claims all campaigns reached their targets at 99 cents per download, with PlayMesh's iFarm game receiving an impressive 56 percent conversion rate on clicks and generating more than 60,000 downloads. On the back of this, iFarm hit the #1 position in the free game chart.

"It's important that our mobile ad network provide an engaging ad format that aligns with our social gaming experience," said PlayMesh founder, Charles Ju.

"After signing up for Greystripe's 99 cent download program, we noticed the conversion rates on iFarm increase almost immediately. We're very pleased with the success of the campaign, and look forward to working with Greystripe in the future."

Greystripe says its program is guaranteed to have no click error because of its opt-in user experience and significantly higher click-through rates due to its proprietary Flash ad format, GS.ImpactDL.

You can find out more about it at the GreyStripe website.