Just how many of those 500+ applications available on Apple's App Store are games? A lot. So many, in fact, that ad-wrapped mobile game distributor Greystripe has come out with an SDK for iPhone game developers that lets them become part of the Greystripe in-game mobile advertising network. The SDK integrates advertising and reporting APIs - and gives the developers an easy way to make money if they decide not to charge for their games.

The move is more than just a way to score new game partners for its network, but a way to keep its existing partners happy as well. According to the company, many of its 120 current publisher partners, including Amplified Games, Xgen Media, DS Effects, United Fun Traders, Relaxas and Norbsoft are getting into the iPhone game and planning to stick with their ad-supported model.

Greystripe's iPhone SDK supports standardized, full-screen square (320x320), giving advertisers a new canvas size for their brand messages in pre-, interstitial and post-roll inventory. Developers can sign up at http://iphone.greystripe.com/register.