You are all getting this wrong. LOL.
ZEN, no, it wouldnt, ebcuae it has software as you say.
External hard drive as first suggested,COULD work, providing could power it. They usually plug into the wall aswell as teh usb for data transfer, OR have 2 usbs, one for power and one for data transfer. Athough they are not good harddrives.
NO your phoen wont work, it has software
Your head unit only uses USB to connect directly to storage, sotorage being blank storage with foldered files, not the operation system of a ZEN or pphone. the only exception is the ones credted for ipods.
So you need to power the hard drive, and im not wrong, speed bumps would ruin the disc. as external hard drives, are just normal dektop hard drives, in a caddy case.
thanks
Mike