You can do one of two things: you can buy a factory phone system and install it (can be found on eBay or elsewhere), then buy the MB bluetooth adapter or you can visit www.eurocarphone.com and get the Argos device which will give wireless connectivity via your MCS unit. I have the factory equipment in my M Class with voice control. It works very well as expected. I have a buddy who has the argos in his ML500 and it works as well. Hope this helps.
Just a note on the Argos - I just installed it in my 2003 ML500. If you never had a phone before, you are going to need a Mercedes part, the so-called Y cable from the completion kit, to install the Argos. EuroCarPhone can sell you the D2B cable, which is part of the Y-cable, but they don't have the non-fiber part. I couldn't get this part from the dealer (and I tried my own dealer and various online dealers), but it may just be that the part number I was using has been updated. So, I bought an older phone completion kit from a classified ad that included the cable. The cable for the 2001-3 M Class is part #Q6820672, but the 2000 year cable works too.