iPhone users are probably not familiar with the feeling of getting an app last, except those that wanted to try Xim. The photo sharing app was announced on all three platforms, but due to Apple's slower acceptance policy has just now been published to the iTunes app store (download link below).
What sets Xim apart from every other mobile picture sharing app is that the people you are sharing with don't need Xim installed. You can simply text or email a link that will open up an interactive Xim session on the browser.
But why download the app then? Well, you need it to start a Xim session. Further, only people with the app can add pictures and people to an existing Xim session. So now the members of your Xim session using iPhones can contribute also.