Format is not really a problem. There are conversion programs out there to change the format. I read ebooks on my smartphone so that is another option.
My phone is Android based and the ebook reader I use is Aldiko, free download from the Android Market. The converter I use to get them to the .epub format is Calibre, another free download for your PC.
My last phone was Windows Mobile based and I used Mobipocket on it, free download, and Mobisoft has a converter to get the books to .prc format.