Micromax Q5 IMEI 910040053734161
Call waiting problem

I have brought my MICROMAX Q5 mobile i month back since i brought the phone from the the call waiting facility is not working as the phone got dual sim and both the sim are active when my first number is busy the there is no call waiting on my other sim either the caller gets silent reply or says the number is not reachable why so there should be a call waiting