Wirelessly posted (Mozilla/5.0 (iPod; U; CPU iPhone OS 4_3 like Mac OS X; en-us) AppleWebKit/533.17.9 (KHTML, like Gecko) Version/5.0.2 Mobile/8F190 Safari/6533.18.5)
if you have the text sound set to "none" and you get a text in lock mode, then it won't vibrate. i just set my text sound to an actual sound and my phone started vibrating in lock mode. hope this helps!
It's not as strong as my old Blackberry Curve. I feel it vibrate about half the time. If I'm not expecting something (like a text response) I often miss it.