Wouldn't it be great to use the Bluetooth-Phone in
conjunction with ISDN4Linux as ISDN-Phone, so You
only have to pay the cheaper ISDN-Charges instead of
the of Your Cellphone-Provider? I don't know if it's
possible, but the other way round (Using another
Bluetooth-Device, eg. a headset, in conjunction with the
cellphone) is already possible. And I know there's a
prototype from Ericsson that provides this requested
feature.