I used to own a convertible and I can tell you from experience that if my phone rang while I was driving with the top down I just didn't answer it Bluetooth or not. The person on the other end would never be able to hear what I was saying because of all the wind noise. A company called iASUS has announced a new throat mic system like you see military and police types in movies wearing that promises to pick up your voice without getting any of that wind noise.
The throat mic is called the NT3 and it pics up the vibrations of the persons voice through their throat rather than having a mic. What that boils down to is that the NT3 system doesn't care how much wind noise is present.
The device has a tangle resistant braided nylon wire, an acoustic coil earpiece and works with any device that has a 2.5mm or 3.5mm headphone jack including the iPhone and more. The mic is available right now, for $89.00 and the only downside I see is that this thing looks strange. I also wonder what your voice sounds like using the throat mic since its picking up voice vibrations at the throat rather than spoken words from your mouth.