In order to boot different OS (apart from Harmattan), you need some "bootloader".
Simple silly bootloader aka
sillyboot, that allow you to choose whether to start alternative OS or not (by pressing Volume Up key).
ONLY FOR EXPERIENCED USERS! NO WARRANTY!
THERE IS VERY HIGH RISC OF GETTING BRICK!Short HOWTO:
1. Put the file attached to the device.
2. Execute following command as root (I suggest to use SSH connection over USB):
tar xjvf /home/user/MyDokumentz/sillyboot.tar.bz2 -C /3. Write full howto for not so experienced hackers;)