I read an article that was posted on Reddit a few days ago about a class in 2008 from Stanford Uni. The class's teacher gave the students an assignment to build a phone app and get people to use it.
Long story short, about a dozen of the students ended up quitting school to continue on with their new business because they were doing so well.
They were all free apps with just add revenue.
edit.. this is the article. Guess it was 2007 not 08.
http://www.nytimes.com/2011/05/08/te...lass.html?_r=0