Just go to http://books.google.com/m in your mobile browser and search for a title, author, or subject (or browse the list of "featured books" and various categories like business and economics, the classics, science and math, travel, etc.)
It's that easy.
If you're familiar with Google Book Search, you'll notice that book previews are composed of page images made by digitizing physical copies of books. These page images work well when viewed from a computer, but are a bit much when viewed on a phone's small screen.
Google's solution to make these books accessible is to extract the text from the page images so it can flow on your mobile browser just like any other web page, a technology called Optical Character Recognition. According to Google, the extraction of text from page images is a difficult engineering task, since "smudges on the physical books' pages, fancy fonts, old fonts, torn pages, etc. can all lead to errors in the extracted text."rites on their blog:
Imperfect OCR is only the first challenge in the ultimate goal of moving from collections of page images to extracted-text based books. Our computer algorithms also have to automatically determine the structure of the book (what are the headers and footers, where images are placed, whether text is verse or prose, and so forth). Getting this right allows us to render the book in a way that follows the format of the original book.
The technical challenges are daunting, but we'll continue to make enhancements to our OCR and book structure extraction technologies. With this launch, we believe that we've taken an important step toward more universal access to books.
To try it out, point your mobile browser to http://books.google.com/m and begin reading. Oh, and if you do bump into some rough patches where the text seems, well, weird, well, you can just tap on the text to see the original page image for that section of text.
Amazon Kindle? According to Google -- and despite Amazon's upcoming announcement of its next-generation device on Monday -- to heck with it!
(Though it should be noted that the Kindle library is largely contemporary, while the Google Books library is, well, a bit dusty.)
UPDATE: Amazon also announced today that it was working on making the titles for the Kindle available on a variety of mobile phones. The company, which is expected to unveil a new version of its e-book reader next week, did not say when Kindle titles would be available on mobile phones.