I just got this set up yesterday, and it took me a minute to figure out, too...

When you receive the call, you click "Answer" and it pops up the new window over the top of the regular Gizmo window. You'll see the Gizmo icon on the left of your screen in your taskbar or whatever it's called now has a box with a "2" in it meaning there are two open windows (the regular gizmo window, and the new window for the call). If you click on that icon, you can select between the two windows. Select the regular Gizmo window, then scroll over to the right through the tabs with the ">" arrow until you get to the dialpad. Tap "1" and you're good to go!

-SG