Lol, so now that Ashley Simpson has her cell phone mounted in her car, you want one too huh? Aawww, that's so cute! =P

Seriously, though I used to have a Motorola T720i with a hands-free car kit in my G. It had the phone cradle where you just plug the phone into there, and it charges the phone. It features an external speaker which was mounted by the passenger-side door and a microphone which was mounted in the top left corner of the windshield. There was also an external antenna that was mounted in the top right corner of the windshield (just a little piece sitting on the inside, doesn't resemble an antenna at all).
Anyways, basically you plug it in and if you wanna make a phone call, just dial the number through your phone (or by accessing your phone book) and you just have a totally hands-free conversation, it's just a speakerphone. Sound quality was just fine and I really liked it (driving manual + talking on cell phone is NOT easy). I had it removed several months ago when I got my new phone. I had these problems with it: I didn't like having that cradle thing there, it made the interior look less "neat". When the phone was plugged in, the backlight was on all the time and it was annoyingly bright when driving around at night.
Basically, what you have to do is just purchase the hands-free car kit for your phone...you can purchase it off of eBay for a better price and then take it to some guy to install it for you. When I had my Motorola T720i, the hands free car kit was like $90 shipped off of eBay, and installation was around $160 or so (I know the install was expensive, but the guy does a flawless job).
Anyways, I hope all this helps. You sounded like you had minimal info on it so I wanted to give you all the facts and the pros & cons that I experienced when I had my kit.

MrElussive
03 G35C 6MT

 

My phone cradle was located exactly where Chris' is. Great location.

MrElussive
03 G35C 6MT