My only mobile experience helping design and document UIs for DOS and Windows CE handheld scanners, so my personal experience is definitely not on the high-end of mobile application design. However, in my rather random research, I have not found what I would consider definitive guidelines. Of course, the iPhone, new generations of iPods, and emerging development for the iPhone platform seems the most likely to set a true standard.
While Apple is an obvious company to follow for great design, another worth following in the mobile computing space is Nokia. I've attended several presentations by Nokia's usability specialists at UPA and other conferences. Check out the usability section of their forums and developer success stories.
An additional idea: Dan Saffer's Designing for Interaction (book); he has general guidelines for creating smart applications and clever devices. I can recommend this book, although I am mainly focused on its content for website design. With that, Dan is about to release his 2nd book, Designing Gestural Interfaces.