I have the Bluetooth in my '08 ML550. Works beautifully with Blackberry 8830, Blackberry Pearl 8130 and LG Chocolate Flip. Phones connect instantly when you start the car, and the convenience can't be beat. Voice quality for you in the car is fantastic, adn voice quality on the other end is pretty good, with road noise muffled well. I like it so much I'm going to add it to my '06 ML500.
Love it in my 2008 ML63. Works great with my Treo700p. Although the entire phone book does not transfer over, all of the quick dials do. Does not transfer any of the contacts from my wife's LG Fusic though. Would highly recommend it.
It is only worth it if you have a phone that works with it. Higher end cell phones will not be fully functional. I would not recommend it unless you already have one of the phones of their list. Nobody bothers to help you if your phone list does not transfer. I don't know why I would have that without the phone list. I have to dial every number as if I recall all the numbers I may ever need to dial. If I have to stop and look up the number, what is the point? I may as well use the payphone of a gas station.
What is more bothersome is that they do not cooperate with companies like nokia LG etc and give them important info to add to the phone software, something like a patch.
I am interested in the Bluetooth module as well and would be willing to participate in a group buy....waiting for my 2008 ML320CDI now, which should be deliverd in March....