First of all you will need a phone that is compatable. Here's a list of phones from a while back that were tested:
http://www.300cforums.com/forums/136849-post24.html
The list may have been updated since then. Basically you have to pair the phone to the uConnect. This is explained very well in the manual. It will communicate up to 30 feet and the voice comes out of the audio system. A very worthwhile option to have. To place a call, just press the button on the mirror and there are a few simple commands you say like "call" or "dial" or "phonebook". Other than that I can't tell you how it works. I can't tell you how a TV works either, but I know how to press a button.
Rambit