1) Application uses mobile network for sending SMS - your mobile operator charge you
2) SMS will be sent only if your voice mail is off
The purpose of this app is to let the caller know that you are doing something important and you can not attend the call. You set an event and a message associated with it. When ever you get a call that you do not attend when the event is on, the caller will be notified with a SMS with the message that you have set.