Audible, which enjoys a near-monopoly in the online digital download market for audiobooks, has tons of audiobooks that can be purchased and downloaded. They also provide a file manager which allows you transfer your audiobooks to a digital rights management (DRM) enabled player, like Apple iPod, Creative Zen, SanDisk Sansa, various GPS devices, and the Amazon Kindle.

What do you do if your MP3 player isn't supported by the Audible manager? like Motorola Droid, HTC Evo 4g, Windows phone 7 series, Creative Zen, Zune, PSP, Sony WalkMan, Blackberry, etc, so if you want to listen to AA files on any device you have, there is a need to Remove DRM from Audible AA format and Convert .AA to MP3.

How to convert Audible AA to MP3 for Droid(X/2), Walkman, Zune(HD), PSP(go), Windows phone 7 serise

This tutorial will tell a quick way to easily convert Audible AA to MP3 files (DRM-free):
Remove DRM from Audible's audio books (Removing copy-protection from .AA files)