Button Assignments on HTC S640 with MS Voice Command 1.6

[fretbuzz]

Hi - Just picked up a HTC S640

http://www.telusmobility.com/on/pcs/handset_htc_s640.shtml

.. and installed MS Voice Command 1.6 on it. I have no idea how to assign a button to Voice Command. I see on the Voice Command setup the option to use buttons "Record" then "App1, App2 ..etc" but I have no idea what these buttons are on the S640? Since the phone uses WM6, I'm not seeing an option to customize buttons in the settings - is this a limitation of WM6?

Thanks for any help!