After some rumblings this past March, Microsoft has now officially joined the iPhone development community with Seadragon Mobile, a free app that lets you "infinite zoom" gigapixel-sized images. Although Seadragon is available as a Silverlight application on the desktop, Microsoft isn't bringing Silverlight to the iPhone, so don't get your hopes up -- this is probably just a custom implementation. We're itching to see if the company has any more apps in the pipeline -- we'll wish for an Office editor, but expect a Minesweeper variant.