Just recently there was a discussion about a UI-less Bluetooth-enabled phone - unfortunately it turned out to be a misunderstanding but I think you'll agree that the discussion is along the same lines as that which you are proposing. I certainly think the N800 could become the central computing, control and storage device for many with Bluetooth accessories providing the audio I/O (A2DP/HSP etc.) and high power radio capabilities (eg. 3G/GSM/EDGE etc. - even WiMAX) which then allows the user to tailor the device to their chosen carrier/network/tarrif etc.