In my 2004 A6, underneath the center armrest, there is a small storage bin, about the size of an ipod id say, about an inch deep..on the top side of this bin (the side facing the dash) there is some sort of plug. What is the function of this plug? Thanks.

 

i'm pretty sure that that was the plug for the optional carphone, because i believe mine has that too. seeing that yours is a '04 though, it might be something completely different, so maybe someone more knowledgeable than me will chime in.