title: Android: How to determine if the number being called is valid or invalid
body: <p>I have a big list of opt-in numbers. 
  Some of them are bogus or fake. </p>
  
  <p>I need to write a small app that does the following:-</p>
  
  <ul>
  <li>Read numbers from an excel file</li>
  <li>Call each number: if the call gets through (the phone rings or is busy/engaged), we mark the number as valid in a new column in the excel sheet. If the number is invalid, we mark the number as invalid.</li>
  </ul>
  
  <p><strong>Is it possible to achieve this in Android?</strong></p>
  
  <p><strong>Can we get the response status while making a call from the app?</strong> 
  Example: Status=Ringing, Status=Busy/Engaged, Status=Invalid etc</p>
  
  <p>Is there a better way of finding if a phone number is valid or invalid?</p>