MCA stands for 'Missed Call Alert'.This service is provided for free by BSNL but the thing is this that it doesn't comes pre-activated,so many user are unable to use this service as they don't know how to activate it.So here is a simple procedure to start it.Remember its free of cost service so you won't be charged a paisa for it-:

1.Go to Call Divert option in the settings menu of your mobile.

2.Divert calls when not reachable,when not answered,when not available to 17010.

3.Your MCA service is all ready.Enjoy!