I added the AUX in jack when I wanted to listen to my phone. The thing about getting another headunit is that I didnt want to go through the hassle of getting the controls on the dash to keep working.

I posted a DIY on adding the AUX in in the modification forum. It was really easy and was $45.

 

I've found that it is perfect for coins. There are slots in there for coins, it's sweet. It's just good for money in general, you can also hold cash and checks in there.

 

No hassle needed. Look into the Modifry DCI.

 

I always assumed it was for holding the radio's user manual.