You are out of luck....
Ford did not have the foresite to specify the unit had to support MP3 and unfortunately they cannot be converted. The best you can do is ugrade the unit to a six stacker if it is not already.
Alternately, you can purchase an AUX input lead from Ford which allows you to play an iPod or similar device through the unit.
If you visit this site, you will see your upgrade options.
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