Sms Responser Pro can assist you when you are busy. The application automatically handles incoming call and sms on behalf of you. You just need to set a response sms and run the application. When a call or sms is coming, the application sends your pre-set message to the caller so they will know you are busy. Later you can browse all missed call and sms in the application.
You can set any response text you like. You can also set black/white number list, auto/manual hang up, etc.