Setting up synce-hal for Bluetooth connections isn't
difficult, it's just not well tested, and may not
turn out to be the 'right' way.

The --enable-bluetooth-support option to configure will
install various support files for ppp as detailed below.
Depending on your distribution, some of these may need
to be moved.

$prefix/ppp/ip-down.d/synce-bt-ipdown
$prefix/ppp/ip-up.d/synce-bt-ipup
$prefix/ppp/peers/synce-bt-peer

You need to run dund with these options

--listen --activesync --msdun call synce-bt-peer

There is probably a method in your distro's boot
sequence to set this to come up automatically.

Finally these services must be added with 'sdptool add'
activesync
dun
sp

Then connect to the PC from the device with the 
ActiveSync over bluetooth option.
