A really useful free resource from those wonderful people at Smashing. Outline is a set of 28 printable sketching and wireframing papers (in PDF) for seven mobile platforms: Android, BlackBerry, iOS (iPad and iPhone), Meego, Symbian, webOS, Windows Phone 7. The set consists of a few combinations, such as actual size, 10 devices fit to a page, and landscape layout. Download it here.