This is an implementation of the handsfree profile.
At the moment you have to use voice settings 0x0060
to have any chance to hear something understandable:
$ hciconfig hci0 voice 0x0060

At least up to kernel 2.4.22 you'll need to apply
Marcel Holtmann's patches (http://bluez.sf.net) to
make SCO audio work correctly.
Starting from Kernel 2.4.24, it should work without
any patches.

Then you have to make sure that arts is set to full 
duplex mode (Control center -> sound & multimedia ->
sound system -> sound i/o -> enable full duplex).
Also check that recording is working and (kmixer, 
artsrec). 

The program integrates with kbluetoothd and will be
started when a phone opens a handsfree connection to
your computer. 


TIP: When you're running KDE 3.2, you can set up kaddressbook 
to use kbthandsfree to dial phone numbers.
Just put 'kbthandsfree --dial --phonenumber %N' under
Settings->configuration->General->Script-Hooks->Phone