My phone is always on silent/vibrate. However I agree with BlackSpyder, people will notice me if I suddenly walked out, mumbling about "my phone..." in certain situations. e.g. I don't have it on while working cus the vibrate seems to make the zips on my pockets buzz! And once I was carrying a tray of hot drinks and I started vibrating....
hehe luckily I kept my balance.
One funny thing happened tho. My English teacher had a v strict no mobiles policy and I ensured my phone was always in silent mode at school. However in English class one day, I dropped my pencil and as I bent down to pick it up, I must have leant on the "Play" Button (I have a Walkman phone) and my tunes started blasting from my pocket
But she was kind enough to return my phone at the end of class after many apologies.... I was so embarrased :| I now ensure that while my phone is set to silent, I have my Walkman volume turned off too! hehe