It is a stereo headset

http://www.bluetake.com/products/BT420EX.htm

I just got one ($160 at ecost.com) and would like to share notes on getting the most out of it.

I needed to install the Carkit update to get the headset to work with Cingular Treo 650.

I can get good stereo playback (realplayer) using the Bluetake's dongle. I can also independently use the BT420 as a handsfree headset (I can hear the rings, answer the phone, hangup).

However, I can't transition easily between listening to music and answering the phone ...

Aloke