During The Conference Call - HTC HD2 User Manual

Chapter 2 Phone Calls 

During the conference call

You can turn on the speakerphone during the conference call by
simply placing your phone face down.
When you tap a participant while the conference call is in progress,
you will see these buttons:
To talk in private with the selected participant, tap the Private button
( ). This separates the participant from the conference call and puts
the others on hold. When you want to swap between the private call
and the conference call, tap the dim area that shows "On Hold".
You can end the private call by tapping or the End Call button at
the bottom of the screen.