Thanks for the URL, it looks like you have a Nokia Stereo Headset HS-43, they are out of stock with Nokia (30 USD) but ebay somtimes has them for 5 USD + about 8 USD for shipping http://cgi.ebay.com/Handsfree-Headse...QQcmdZViewItem .

I did some more research but I've not worked out the API to detect the regular microphone button :-(

http://www.internettablettalk.com/fo...ad.php?t=12143 and http://www.internettablettalk.com/fo...0&postcount=17 speculate the regular button grounds out the Mic line (seems reasonable). I wonder if it is worth posting on the developers mailing list about how the regular button is detected and then see if the API can be called differently.