I think something like http://chaos.allsiemens.com/siefs/ but for the Nokia USB cable would be ideal.
As it is userspace, there would be no need to release the code, as the linking tool could be a separate binary.

If my linux box could auto-mount the phone as a local filesystem over BT/IR or preferably USB, then i could script things like remote incremental backups. Or podcasting/syncing content.

Also, is the DKU-2 USB protocol documented anywhere?