I have a 2003 S430, using the Bluetooth puck to link my cellphone to the car's COMMAND system.

I had two problems:

- The COMMAND system would download my cellphone phonebook, but insisted on using the PO's (Previous Owner's) phonebook from the COMMAND system instead. I erased his numbers, but couldn't get the car to use the numbers from the cellphone.
A friend (who also owns an S430) and I jointly bought a Chinese MB Star system. I spend some time going thru some of the things that we could do with the system, and discovered that I could tell COMMAND to install a phone with enhanced capabilities. Problem solved - the COMMAND now downloads and uses the phonebook from my cellphone (the same phone). I don't yet know if I gained any other benefits.

- The system suddenly developed problems. First, everything was normal, except that the person on the other end of the call could not hear me. It was just as if the car mike was muted. Pushing buttons didn't help.
In a few days, the situation changed. As soon as the phone connected, I got squeals and static - totally useless.
Searching the forums didn't give any answers. I finally decided that it had be be a faulty connection or a broken wire, and that the curly cord on the puck was the most likely suspect. I removed the cord and rang it out while twisting and pulling. Not the problem. I reassembled it, and the phone and car would no longer pair.
A few minutes investigation showed that the problem was the connector between the Bluetooth puck and its cradle. I pressed the puck more firmly into the cradle, and it worked - as long as I held it. Pressed it firmly in, and applied black electrical tape around the puck. Problem solved. I suppose that I should have used duct tape, but the electrical tape looked better...