I have been very happy with the Jabra JX-10 hands free bluetooth headseat I bought. So happy, in fact, I have decided not to get the car's bluetooth interface.
Although my Sprint PPC 6700 PocketPC PDA phone was not on the compatibility list on Jabra's site, it works just fine!
The JX-10 has digital signal processing to do background noise cancellation. Here is what I have found:
Windows Up, Plexiglass Windscreen installed, normal conversation up to 70 MPH. 75 to 80 MPH can hear both ways but strained.
Windows Up, No Windscreen, normal conversation up to 65 MPH, strained 65 to 70.
Windows Down, No Windscreen, normal conversation up to 45 MPH, strained 45 to 55.
My phone has voice dialing (and reads appointments to you, etc. with Microsoft Voice 1.5) and I do not have to program each one, it converts. Along with the ability to answer with the hands free, it took away any benefit the Mercedes Bluetooth package would add, except muting radio, of course.
It weighs less then an ounce. You can read more here:
http://www.jabra.com/JabraCMS/NA/EN/.../JabraJX10.htm