VoxyPAD (free) is an innovative and easy to use app for sharing and annotating documents, photos and web pages with others while talking about those shared items in real time.
VoxyPad features instant messaging and you can send a message to another user even if they are not running the app. I can see lots of uses for VoxyPAD both in business and the consumer space. You can share a photo while you draw arrows or highlight parts you want to point out to someone else. The app has a built-in Web browser, so people can discuss a web site design or content on a web page. You can draw with your finger to simulate a pen, while others see what is happening in real time. VoxyPad supports up to 5 people in a group chat.
Other functions include the ability to display and annotate maps, and text can be typed onscreen in a variety of styles and colors.
I tried VoxyPad with a friend, and in general it worked pretty well. Pictures could be loaded and shared, then drawings or other symbols could be added by using a finger as a "stylus". The app was pretty responsive over an Internet connection.