Perhaps it's not surprising that the focus of most iPhone games analysis concerns the performance of paid products.

They're more high profile, but as business models on the App Store fragment, plenty of companies are proving there are lots of other ways to succeed.

One of the prime examples is US outfit Backflip Studios, which has leveraged its catalog of free games to generate a massive number of monthly impressions, which it uses either to promote its paid games or to sell to thirdparty advertising networks such as AdMob or Quattro.

In order to keep growing however, it needs to keep releasing free games, and it's finding an insatiable audience for its wares.

Strike every time

Latest release Strike Knight has been downloaded 1.5 million times in ten days and is in the top 10 free game charts in 60 countries.

"We've been extremely happy with the launch and the level of usage," says Backflip CEO Julian Farrior.

"We are currently seeing roughly 500,000 sessions a day at about 5 minutes each from 250,000 unique daily users.

"This equates to about 1,750,000 ad impressions a day on gameplay pages with an average click through rate of 2.25 percent."

And Backflip is continuing to roll out more content, with its most popular game Paper Toss coming to iPad, and new free games Grafitti Ball, Ninjump and Buganoids planned for iPhone in June.