How can I set my phone to just vibrate? No sound; just vibration. I just got the upgraded version of the S2, and my phone won't vibrate. I tried everything.
System > Sound > Ring mode > Vibrate.
Do you have the "quick toggles" in your notification area when you "drag down" the notification bar (IMHO the S2 has this by default)?
SGS2 Notification Area (click image to enlarge)
If so, simply tap the "speaker symbol" there to switch modes between "ringtone", "vibrate", and "silent" (the symbol then will switch as well to indicate the current mode).