If you are talking about headset button which we generally use to recieve the call then you can send one of your own defined scancode to platform and then platform will convert that scancode to keycode.You should add your defined keys in keycodelabels.h and some other files.For adding your keys to framework.According to android,OEM can define their own keys and change some files to get those keys in framework or send it to application.So that application can take action on that.In your case it would be phone app which needs to get this key and take action like hanging up the call.
Check this link. http://pdk.android.com/online-pdk/guide/keymaps_keyboard_input.html -- unsubscribe: [email protected] website: http://groups.google.com/group/android-porting
