Missed call alerts when phone busy on another call?

I have a Samsung Galaxy Y phone with Gingerbread. I have just discovered that I do not receive any kind of missed call notifications when my phone is busy on another call. I am quite shocked as this facility is available even in very cheap, ordinary phones. How do I fix it? Is it because of some phone settings of mine? or is there an android update? or do I need to install some app? or is the trouble with my network operator?