HTC HD2 User Manual page 44

 Chapter 1 Getting Started
On certain screens wherein some onscreen controls or icons appear
small and hard to tap on, you can also use pinch zooming to zoom
in and out. After zooming in, the onscreen control or icon becomes
larger and you can easily tap it with your finger. You will also see
a small preview window, and you can drag your finger around this
window to pan around the zoomed screen.
Normal screen Zoomed screen