I upgraded by HTC Mogul from Sprint to latest firmware from here which fixes some BT issues:
http://www.america.htc.com/support/mogul/s...-downloads.html

After that, my Bluetooth seems to work well in the car. The address book transfers fully which I wasn't expecting but it's a nice bonus. I haven't done any long calls on BT so not sure about that yet. I have noticed a lag in BT performance for dialing & hangup compared with my Verizon Wireless Motorola E815.

Will try to report back again once I have more experience with it. I might even make an attempt to hack together a cradle for the phone but don't hold your breath.