smart have recognised the need for a standard auxiliary connection on the headunit and have provided an mp3 connection with the following part number:

A 454 820 05 51

First off, you need to remove the radio.

As standard, the socket fits inside the glovebox on this side wall. You will need to carefully drill a 17mm diameter hole.

Feed the mp3 socket through the framework and push it out through the panel.

Push the front of the socket to lock the frame into place.

Simply plug the lead into the back of the radio.

Refit the radio and test by pressing the SRC button so that is displays "AUX".