I really tried hard to find the call waiting option in my Android phone. Couple of blogs says ICS completely removed this feature from settings. Really cursed my self to find call waiting/call barring feature in my Micromax A90S super phone
ICS moved this feature from settings menu to call logs :)
How to find Call Settings in ICS ?
Click on call logs and select the "call settings" as shown in the below screen shot
Select Voice Call as shown in the below screen shot
Select Additional Settings as shown in the below screen shot
Select the Target Sim card - My phone is dual sim, ignore this if not applicable
Here's the Call Waiting !!!
Hope this saved your time :0