Some users have reported that, after they update their Samsung Galaxy S2 to ICS 4.0.3, vibration completely vanishes on the phone. I also faced the same problem. Till now, no specific reason why it happens and any update has been given by Samsung that recifies the problem. I rectified the problem using the following steps: a. Firstly put the phone in silent mode. (Even if doesnot vibrates). b. Switch off the phone. c. Switch on the phone. While the operating system loads, you will notice a small vibration at the start. If this happens, the phone's vibration facility will function properly. Normally the problem doesnot occur again. But if it occurs, repeat the same steps again. Why it happens, there is no logical reason to explain, but in my case it worked. Please try this method if you face this same problem and share your experience.