title: How to make number not reachable (similar to call blocker)?
body: <p>There are lot of call blocking application for mobile, like NQ Call Blocker. But in these applications, if we add a number to blacklist, the caller will hear "Busy Tone". Also the caller can hear "Ringing Tone" for a fraction of second. Which means, it'd look like we are rejecting the call intentionally.</p>
  
  <p>Now, what I'm trying is, to develop an call blocking application, which can send "Not Reachable Tone", instead of "Busy Tone" ... ??</p>
  
  <p>For example, call your mobile from another number, when it's ringing, try to change your mode to "Airplane Mode". You'll hear "Not Reachable Tone". [Possible in some android device, long press the power button, and activate "Airplane mode", when your mobile is ringing.]</p>