I'm deviating from the norm here to do a review of an audio book app for three reasons. One, it's a great app. Two, I'm getting married in a few months and I barely have time even for audio books. Three, a lot of the classics I have reviewed are available on the LibriVox app, so it makes it easy for you, potential reader, to get caught up on what I'm going on about.
I am only able to speak to the LibriVox app's usefulness on the iPhone. I currently have an iPhone 4. The app was free at the app store because every single book on it is in the public domain. The great thing is that the recordings that people do for the app are also put in the public domain, so you can use them if you have say a book blog and want to put a sample of a book up.
Using the LibriVox app is easy and I do it just about every night. You open the app by clicking it and then either choose a book from your favorites or use the browse catalog or search function to find a book you want to listen to. They are typically broken up into chapters, sections or stories. You can click directly on those parts to skip or you can start from the beginning. Inside the book, you will see a timer function. I use this so the app will stop running on my phone after I fall asleep. A warning, though. The "resume" function does not work for me if I use the timer. You may have to remember where you left off.
The books on the LibriVox app are primarily classics. This is because these books are without copyright, so volunteers for LibriVox can read them and offer the recordings free. You will find a wealth of books from authors like Sir Arthur Conan Doyle and H.G. Wells. You will also find obscure self-help books, science fiction and some newer novels that have somehow made into the public domain marketplace. There is definitely a limit to how many good books you will be able to listen to from LibriVox, but I haven't reached it in nearly a year, so you will have some time with this app. Enjoy it.