Document format for smartphone

I'm going to 开发者_高级运维build an ebook reader for smartphone (Android&iOS). But i don't have any experience about ebook format for smartphone. This's smartphone application which can use to read ebook format file. What format type should be used (PRC, PDF or ...)? Is there any library (for java and objective-C) support to do that?

Epublib for Java: http://www.siegmann.nl/epublib