When you can view something for free on the internet, you can make a safe bet that there is going to be some sort of advertising supporting its freeness. I have enjoyed a free app of Mancala for the iPhone 3G for quite some time now, and am not discouraged from playing just because I may have to wait for an ad to show up in between every third game.

I have actually come to like the ads, because they've been changing over the last few months.

Below is an ad that has appeared for quite some time. Although the actual product/organization ads change frequently, this has been a common format.

In contrast, the below image is an ad that I saw just today while playing a rousing game of Mancala while watching a little television. The ad format has changed so much in so little time. I am curious as to where it will go next!

There is an article I read recently calling for the creation of an ad for any iPhone App. Apparently the AdHack community has had success in the past creating iPhone apps ads and so there is a promotion going on catering to this. It seems you can submit your ads to Macworld and they will help get the distribution setup to connect ad buyers with the creators. Seems intriguing if you are a talented developer!