Is there any tool available to properly wipe empty storage space on N900, before you sell it or give it to someone else? I suppose that resetting it to default settings is one thing, which should be followed by some DoD compliant safe wipe.

The memory card is no fuss, as you can probably just put it into a card reader and use sdelete or similar on a Windows computer to wipe it. Could the same apply to the onboard storage (i.e. you connect N900 as "mass storage", and use sdelete on that "drive"), or is there a better solution?