From http://www.htc.com/www/htcsense/index.html :
"Ever fumbled with your phone because it went off at full-blast during a meeting? Well, don't worry! Now as soon as you lift your phone up to see who's calling, the ringer volume gets lower. Want it silenced completely? Just flip it over."
I lost it at some point and, not remembering the app name, have failed to re-download it.
From http://www.htc.com/www/htcsense/index.html :
"Ever fumbled with your phone because it went off at full-blast during a meeting? Well, don't worry! Now as soon as you lift your phone up to see who's calling, the ringer volume gets lower. Want it silenced completely? Just flip it over."