cascada Mobile now offers TAG referral distribution technology. Now this really isn't P2P. They call it P2P because a user can use it to contact another user ... but he has to go through their server.

Still, mobile P2P presents an interesting challenge due to the limited resources on a phone compared to a PC. Plus phones have different operating system and capabilities. Developers have to translate the display for each phone model. Designers either limit functionality so the app will work across a wide swath of phones, or more typically route the phone client into a server somewhere. This does the latter.

More on Cascada:

"Cascada Mobile, a provider of technology for peer-to-peer mobile content distribution, announced the Cascada TAG referral distribution technology. TAG provides mobile content publishers and developers with a solution to enable instantaneous referral of content between any mobile subscriber and their peers.

TAG works by providing publishers and developers with an API that is embedded into any J2ME game or application. Once a subscriber purchases and downloads the application, he can at any time refer or recommend the application to his peers by selecting the recommend menu option embedded in the application. The TAG system then takes care of notifying the intended recipients of the recommendation and determining the version and location of the application that will be compatible with the recipient's mobile device and carrier.

The process of integrating the TAG SDK generally takes less than five hours, including testing. TAG provides flexibility on how and when a referral can be initiated, either from a game menu or as the result of an event in the application. Because the integration takes place in development, developers can match the "recommend" to a friend feature with the look and feel of the application. The SDK also includes reporting features in order to track customer referral behavior."