Syquest,
Your explanation does not work! When you press the handsfree/mute button, all it does is mute the mic on the headset; press it again and it "unmutes" the mic. The handset is completely disabled (and speakerphone, for that matter) when headset is plugged into the headset jack. When a call comes in, the speach path comes thru the headset if you push the incoming line button or press speakerphone/mute button. If you lift the handset, you get nothing, just dead. If you press the handsfree/mute button, it mutes the headset mic. The only way to enable the handset, is to physically unplug the headset from the headset jack.