I'll be posting information on how to add an auxiliary input to your 1998 – 2002 Saab 9-3 and 2003 9-3 Convertible, 1994 – 1998 Saab 900 (?) (and similar vehicles), by using the CD Changer (CDC) lines in the trunk. These lines need to be turned on by the car. The car turns these lines on when a special code is sent along the I-Bus. This isn't terribly hard, and not even terribly expensive.
I got most of my information from the following site:
And the few pieces of hardware I'm using:
SecuDuino CANBUS adapter (~$50)
RBBB Kit ($17)(any Arduino board will work)
FTDI cable ($15)(like this one, but there are several available)
Bluetooth stereo audio receiver ($25)
Stereo ground loop isolator ($40)
Other than that, it's just a matter of connecting everything and programming the Arduino. Once that's done, you just power everything up, connect your device to the bluetooth device, and play your music!