Application

If I am busy and cannot take incoming call, the app should respond automatically with greeting message, either prerecorded or in my own voice and ask the caller to keep a message, which I can hear once I am free. 

Basically it is a Smart Secretary feature for Android phones, I am looking for. 

Pl update me in case someone know about it.

I don't want to use voicemail services provided by the service provider, Airtel.