For Nokia C7, hotkey selection is limited to red-green-menu-camera keys. Why don't make VoiceCommand and Volume keys selectable for hotkey? Especially would be useful to select unused Voice Command key as a hotkey. Menu key is not good for this purpose because when I press it, menu appears.
Volume keys are specially used by the phone itself to control sound volumn. In many cases when you press a volumn key Symbian OS "swallows the event", it doesn't notify the application, so it can't be used.
In Boldbeast Recorder many users select to use "Press Application Key three times quickly" as the hot key on their Nokia C7-00, you may try it.
Yes, but why don't use Voice Command key which is between two volume keys? Not many people really use voice commands, and this key remains unused.
There is no public API for developers to use the Voice Command key.