The idea is to use our old iphones as controllers for the N900.
It could act as a game controller.
It could be a media controller strapped to your steering wheel or handheld that would make for safer driving.
It could be used to control a gps app.
I am thinking it could have multiple modes. Just a touchpad, just a keypad, or a touchpad and keypad for the n900.
Specific modes where it acts as a ps3 controller for the n900, or a gui built specifically to control the media and gps apps of the n900.