has announced their entry into the game. From the press release
Each book displays as an icon on the Home screen. Users will appreciate how books automatically remember where they've left off, particularly when changing songs or even answering the phone. Any page may be easily bookmarked to revisit later, or make notes on any page.
This suggests to me that each book is sold as an individual app through the App store...if so, that seems like a pretty backward way of doing it, though it does solve the 'how do I get it on my device' question. Still, the implied lack of real library management makes this little more than a curious experiment.