Mobile Network disconnects during an incoming call My mobile network normally remains connected so I can use apps like chat, whatsapp etc. However, during an incoming call the mobile network gets disconnected. Is this normal behavior ? 

There is an app called TrueCaller that is supposed to show the caller details when there's incoming call from an unknown number. But since the mobile network disconnects during an incoming call this app always fails to show the name and shows an error message "unable to connect". It seems the normal behavior is for the network to remain connected during an incoming call.

I'm using Android Jelly Bean, 4.2.1. And previously had used Gingerbread (2.2.3) and Froyo (2.2.1). I experienced the same problem in all these 3 OSes.
This is normal if you are using a CDMA carrier, such as Verizon or Sprint.  GSM carriers like AT&amp;T and T-Mobile can allow simultaneous voice and data, but CDMA cannot.  This is supposed to change with LTE devices, although last a checked it wasn't working with all of them on Verizon.  If you have a CDMA 3G only device it won't work.  I'm not positive but I think even with an LTE device on Verizon that supports simultaneous voice and data it still won't work if you are out of LTE coverage area.  I used to work for Verizon until a few months ago and this seemed to be the case.