I had this problem before ICS and the update didn't fix the issue. What will happen is my sound will stop working. It seems like it happens most when smart actions has turned my phone to silent while at work and then the time frame ends and sound is supposed to be on again. Is this a known issue? Only a reboot makes the sound work again. And it's not like the sound shows as being off or on vibrate in the notification bar. Sound will be turned all the way up, but no ringing, notification sounds, or media sounds will come through the speakers. It could also be related to removing the phone from the car dock but I'm not sure.