I have been told that there were some 8/04 build '04's (in 9/04 they started building '05's) that actually were originally spec'ed with the -993 Combo Assist/BT TCU, but that the cars were not coded properly to recognize the bluetooth. If the TCU in your car ends in -993, you should be able to have it activated by re-coding. If it does not, you will need to replace the TCU with a combo unit as UCREW suggests, and the newest version of that piece is the -114 version. Good luck, and let us know what you have
-- fellow 8/04 build 4.4 owner.