it would be cool if there was a button.
ESI has a similar function. You press a button to enable this feature but when the customer starts leaving a message, the button starts flashing and the PBX intercoms the phone and as the user is leaving the voicemail it is played over the intercom 50% volume. then the user can pick up the handset and take over the call. or hit X and drop the call so they can keep leaving the voicemail.
be cool if it functioned similar.