I would like to suggest that Geek Wave support a Bluetooth Hands Free profile or similar.
This would work in two ways.
First as a hands free kit for your phone so your audio playback integrates seamlessly, to make and receive calls, mute, put on hold etc.
Second to connect to an external Hands Free kit possibly in your car. Then as above pass through the phone features from the external hands free kit to the connected phone.
I believe this would be a popular feature among those who use mobile phones.
If a mic input were to be implemented to allow a wired hands free profile. Then I would suggest a stereo mic set-up to match the balanced headphones. In my opinion, that should be a headache for another time, the next generation perhaps.