Can't get my iPhone to vibrate on incoming emails (Japan uses real email instead of SMS text). I have the master switch set to silent, and emails switched to "off" in the sounds settings, with vibrate turned to "on" in those settings. Nonetheless, the phone simply won't vibrate when I receive an email, and I can't figure out why. I've tried multiple different sound settings combinations and still, it won't vibrate on an incoming email. Tips?