my high school wouldn't let you use them at all, i did the usual, duck and txt technique, or the hoodie with bluetooth headset (Jawbone+wisper=perfect) technique... both worked extremly well.
in college, were free to use them, but i have morals, and if i do get a call, it's on vibrate and i step outside the class to take the call (i work for AT&T and do auditing for 7 stores in the Charlotte area in NC. so i do get quite a few calls during the day)
i also saw this a few days ago, might be a good read
http://arstechnica.com/news.ars/post...s-for-you.html