I was getting complaints from people that they couldn't hear me properly through the bluetooth system. So I searched for a while, and found out this "secret" menu in the multimedia system to adjust the bluetooth and a few more things. Not to sure if it has been mentioned already over here, but here is what you need to do to activate the menu:

1. Engine ON
2. Headlights off
3. Press and hold the info button down
4. While holding the info button down, move headlights from OFF to Parking lights and viceversa 3 or 4 times
5. The menu should come up
6. To exit, hold DISP for 3 secs.

Hope this helps!

PS: The menu is intended for professional techinicians, so I wouldn't touch many settings unless you know what you are doing. It probably works on all IS models.