Hi, this is a problem that we see quite a bit on Mercedes - officially there is no support to download the address book from your phone to your C Class. This is a limitation of the iphone and not the Mercedes system. The iphone does not support the standard business card transfer feature which the car needs to receive the contacts from your phone.
There is however a work around which requires a pcmcia card adapter with an SD memory card - you will also need the full version of Microsoft office to transfer the contacts to your car
First of all on your home computer you need to open iTunes and select "sync contacts with" and select outlook from the menu
you need to the open Microsoft Outlook and go into the contacts tab
you should see the contacts that were synced from your phone via itunes
Right click on each contact in turn (you have to save each one individually)and select "message save"
set the destination folder as your SD card
ensure the format is vcard .vcf
this will then save the contacts to the sd card
on the front of your radio is a pcmcia card slot - insert the adapter with the SD card in here
press the telephone hang up, 7 & 9 together to open the dealer menu on your radio
select user data
select read from pcmcia
the data is written to the car
Note - I have only tried this with COMAND vehicles - I am unsure if this is the same on audio 20 units
I would also recommend the pcmcia adapter and SD card is a genuine Mercedes one as some non genuine cards are not compatible
I know this is a bit of a long job but it is a workaround and the official answer is the transfer of contacts is NOT supported with the iphone!
Best regards, Paul