It has to be a scalable community driven website that enables  a designer to design(create edit) themes for all mobile devices and able to publish them... also they should be able to create their own profile...themes should be treated as the main content of the website which has to be downloaded by a registered user or a visitor with a limit.the themes have to categorized according to categories like celebs,automobiles,etc.also to be categorized platform and specific phone model wise...should have a commenting and a rating system with the friend adding system with a in-site message system...and a E-mail notifications system...for reference have a look at gallery.mobile9.com