A quick guide for those who want to use Facebook messages without downloading facebook messenger.
Uninstall Facebook messenger (if you have it installed)
Make sure you have Unknown sources enabled from device settings
Install the attached apk (hello world application) or create a new (empty) android project with the package name com.facebook.orca
As long as the only validation that the facebook app does is checking to find if an app with package name com.facebook.orca is installed on the phone this should work.