Assuming it follows the same model as other platforms, the Instagram app will allows users to take pictures from within the app, or select them from their gallery. These can be captioned, tagged, and have a number of different styles and looks applied through the filter system. Following that, they'll be uploaded to the Instagram service and shared with your friends on the site, as well as the option to share with Facebook, Tumblr, Flilckr, Twitter, and Foursquare.
While there is no word on exclusivity to Nokia for Instagram, the implication of "Nokia and Microsoft have been working closely with Instagram" certainly leaves it on the table as an option.
We'll have more on both these apps in the near future when more details are available - even a screenshot or two would be nice, right now we just have the official company logos on the Abu Dhabi stage.
But what we do have is (finally) a clear and unambiguous message on Windows Phone's 'bogey' app. Instagram is coming to Windows Phone... in the next few weeks. My only wish was that Nokia could have said 'and it's in the Windows Phone store right now' for the full PR splash.