Mailing the story:

Reasons for using a reverse shell include: you can bypass firewalls, you can connect to your phone without knowing the ip, the connection is initiated from the phone so you don't need to have a ssh server listening on your phone. Just think of all the fun this makes possible! As the android phone has a build in shell, it's actually possible to install a console emulator from android market, giving you local shell access. Even gaining root access is really easy.