One useful feature that I found myself using a lot is the # key which you can press and hold down to change your phone to SILENT mode and back out to GENERAL mode. Very useful when you are going into a Church or theatre, rather than pressing down on the OFF key and having to wait for your phone to reboot later (and we all know how long THAT takes!!!)
Another feature which I should add as another post but I won't is the SILENCE mode which you can switch to when people are calling you. Imagine you are in a great conversation with someone and before the other person realizes that your phone is going off, you want to turn it off... but you don't want ot upset the person by rejecting their call (that's so rude!) so you can press the right navi key and stop the phone ringing and vibrating.
EVEN BETTER is the send SMS feature. You can preset an SMS to send to people when you want to let them know u cant take the call now but you will call them back. Also very professional feature.. so you don't lose business contacts and friends just because they called at a bad time... well hope you find those tips useful.