I had the same problem you describe. AudioManager has worked for me. If you're interested, it's available at the Android Market.An app that if you put your phone screen down silences your phone. One that works right. I've tried the 2 I found on the market. One works only sometimes, the other starts working about half way into the sound, not cool in times you need your phone to be silent in hurry or don't want to have to remember to set it on/off
Support Our Troops!! UltraKeyboarded from a wifi monolith.