All you need to do is swap the TCU. The link that abster641 posted is the best reference for TCU part numbers I have seen. Your TCU, part number 84.11-6 945 940, had one month of production from March 2004 - April 2004. Bluetooth is first confirmed in TCUs starting September 2004. And, voice recognition did not arrive until March 2005.

Furthermore, the BMW Service Information bulletin SI B84 13 04 explains that your car was produced too early to have Bluetooth. Here are a couple quotes...

The E53 did not get Assist with Integrated Bluetooth until carsproduced from "10/04 production with Premium Package (ZPP) or BMW Assist (SA 639)."

And, further in the SIB, there is the encouraging upgrade statement "E53 vehicles produced between 3/2004 and 8/2004 are equipped with a TCU that does not support Bluetooth. On these vehicles, the TCU can be replaced at the customer's expense with a 2005 MY TCU. Cradles may not be added to these vehicles because of wiring incompatibility."

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2000 E38 750iL Highline Edition, Upgraded with the lastest 2006 X5 Electronics
MKIV Navigation, 16:9 Display, Bluetooth, TV/Video with Backup Camera, Sirius, and Aux Input