There are plenty of free android and iOS apps that let's you read eBook from your internal storage.
For Android, you can use apps like: Cool Reader, FBReader, Google Play Book.
and for iPhone you can use apps like: iBook (Comes pre-installed), Bookari, and Marvin.
Where you can download these apps? Well you can download Android apps from Google play store and iPhone or iOS apps from Apple App Store.
Please remember that these apps only work if you have eBooks downloaded on your device.
Incase you don't have any eBook downloaded you can download free eBooks from torrent sites. Few of the best torrent sites for eBook can be found on this website- http://mmxnewscaster.com/top-free-ebook-torrents-s...