Guys....the bottom line is that MOST Hero users I've spoken to (myself included) actually DO have problems with accidentally hanging up on people or touching other buttons on the screen with this phone. It's a real oversight....
Apple, the pioneer of the touch screen smartphone, correctly realized from DAY ONE of their research that accidentally touching the screen with your cheek was going to be a major obstacle towards making the device usable for the great majority of people. They smartly developed a solution based on incorporating existing proximity sensor technology.
Stop arguing this point...99% of phone engineers would tell you that a proximity sensor is an absolute necessity for a phone like this. I was stunned when I discovered the Hero didn't have one. I misread a review or two before buying it and just didn't realize...oh well, waiting for the Samsung Galaxy now.