OK, here is how mics work.
The type of mic in a BT system is an electret condenser, it has two or three terminals, the mic is basically powered by a Positive (+) voltage, either applied to the tip, or if your mic has 3 connections then voltage is applied to the element and audio is taken from the output of the element via a capacitor to block the voltage going into the preamp or in some cases the voltage biases the input of the amplifier stage. For further info, Google is your friend.
My first question is why do you want to replace the factory mic? The factory mic is tuned and filtered to eliminate low frequency sub sonic sound and is probably a pretty good mic. And usually there are two mics a dipole setup that is used for noise canceling. I haven't looked at the factory service manual but I'm pretty sure unless you are putting in an aftermarket head unit that comes with it's own system optimized microphone you would probably be better off leaving it alone. Besides that the factory BT and the mic are mated together as a designed package system. Could you put a more expensive mic in there? Sure, but you probably wouldn't realize the dollar amount of improvement in the cabin of a sports car. The best possible setup would be an over the ear with a mic element at your mouth.
http://en.wikipedia.org/wiki/File:El..._schematic.png
