I have a phone with iBooks installed, and I have read a lot of non-DRM epubs on this device. I wonder if it is possible to back those books up? I couldn't find any relevant menu neither in the software nor in iTunes.
If you sync your phone to your computer, you should be able to see all your files in this location:
Use a terminal to go there, or press CMD+Shift+G in Finder and paste in the path.
Note that your books will not be named as titles but rather the hash of the file. With some basic plist hacking and bash scripting you can rename them so something useful, or just throw them into Calibre and let it do it's thing.