The format of mobile e-books varied according to the brand, model, and operating system of the phone. But generally speaking, the common mobile e-book format was: 1 txt1: txt1 is a simple text file format that can be read on most mobile phones and computers. 2. java.com is an application for reading e-books that runs on many smart phones and tablets. 3. Amazon's Kindle format: The Kindle format is an e-book format based on the Amazon platform that can only be purchased and read on the Amazon website. 4. E-book format: The e-book format is a more complex format that can support a variety of text and image format and can be read on many mobile phones and computers. In addition, there are some third-party e-book format such as azw, mobi, chm, etc., which are also widely used for mobile e-book reading.