Greetings and welcome to X5World, Gonzo
On phone systems you can either go the OEM route or the aftermarket route. Going OEM will give you benefits such as steering wheel controls and integration with the nav system and radio.
The Bluetooth system is the latest and greatest OEM solution that BMW offers. Unfortunately for you, since it looks like Unicel uses CDMA technology in its network, your choice of available handsets that have Bluetooth is somewhat limited as compared to phones that work on GSM networks. There is a wealth of information on Bluetooth at
http://www.xoutpost.com/bluetooth.htm, including retrofits into a 2001 and 2002 X5. I would also encourage you to look at
http://www.bmwtransact.com/bluetooth/index.htm to get a better understanding of this integrated phone system.
Another alternative is to install the CPT8000 (based on the Motorola Startac/Timeport phone, which is manufacturer discontinued) or the CPT9000 (based on the Motorola V60). Info on these systems can be found at
http://www.xoutpost.com/cpt%20info.htm
Good luck and again, welcome to X5World
