As a start, I intend to use short txt messages. There are limitations here on the number of characters (not more than 120) and small screen size of mobile phones that only have a txt messaging function. I am keen to push the envelope to see how this technology can be improved. Using flashcard type displays will be an option.
Moving beyond just using SMS txting, I am attracted to the concept of using more visual displays. These do not necessarily have to be colourful displays done in flashlite but simple scrolled comic strips. The Japanese have a lucrative market in manga comics distributed on cell phones as reported by all about mobile life. There is also a link from mobile life to test if manga is displayable on your mobile...
I have also found several good articles on how to set up content on to mobile phones
This web page has an especially succinct guide on developing content for mobile phones. Another good resource has been one on how to make small devices look good with other articles via the main page of an opera group on development of mobile content.