We have done this before but we fitted a Mercedes bluetooth unit that clips in the phone holder where the old phone would go.This is the easiest option.

This means that you will still be able to use all the steering wheel buttons for the phone operation etc.

It all depends what audio/command unit you have as to how many functions will work ie scrolling phonebook in das cluster etc.It also depends on phone model.There is no hard data on what is better that others.

This part is on back order at the moment but some dealers have stock.Get your local dealer to do a dealer search in your location.

Part number B6 78 75 877 about £215.

There is a company called Braybrooks that specialise in Mercedes Audio (but I do not have any reccomendation) They do conversion to the newer UHI (universal handy interface) .This means that your car has just a small mounting slide and you just buy a new bracket when you change phones.It came out in 2004 !