USA Mercedes Command systems download the phonebook from your phone everytime the system is powered up and/or a phone is "connected." You don't do anything. Command does not "save" anything from your phone.
If yours doesn't work, it means your phone isn't compatible.
That isn't completely accurate. The US W221 for example does have a local phone book. You can store phone book entries that are available even if the phone was not in the cradle (in the car). I did not check this really for the W204 but I'm pretty sure it has the same functionality (and some more).
The COMAND phone book contains all address book entries that have at least one telephone number. COMAND also reads the phone book entries stored in the phone book on the mobile phone and displays them in the COMAND phone book.
If there is an entry stored both in the address book and in the phone book of the mobile phone, the COMAND phone book will only display the address book entry.
Calling up the COMAND phone book
The COMAND phone book appears.
Phone book with name display and smart speller activated
To change the phone book display
To call up options
Icon for the phone book on the mobile phone
To close the phone book
Voice entry icon