Samsung R500 - text message beep

Just got this phone. If i am in a texting window, and i recieve a new text message, the phone beeps (instead of ringing/vibrating) no matter what the ringer volume/vibration/off. I need to be able to turn the beep off so that i can text in class while not having to worry about recieving a text. Help?

Try to activate silent mode push and hold the volume down key, to deactivate it push and hold volume up key.