For phone calls or just playing music? For music, you can just get an AUX cord for ~$10 that goes from the phone's headphone jack to the car's AUX input in the stereo head unit (where volume, radio controls, etc. are).
The 2008 DTS does not have Bluetooth, sorry. You'll either have to get an after-market Bluetooth kit or replace your VCIM with one from a newer model year. I would have loved Bluetooth, but 2009 models and up within a reasonable distance were out of my price range unless I got one with way more miles.