If people always call you when you are occupied ( meeting, personal occupations, ... )
If you keep up to date your local android calendar.
If you want to optimize your calling schedule so people calls you when you are available.
What is it ?
An application which works in background when activated.
An application which, if you are busy when someone calls you, send him an sms with a time period to call you back
How does it works ?
It checks the Android calendar to know when you are available.