title: What's meant by result errors of SmsManager?
body: <p>When I send an SMS using <code>SmsManager</code>, the result intent broadcasted holds a value of 5</p>
  
  <pre><code>Activity.RESULT_OK
  SmsManager.RESULT_ERROR_GENERIC_FAILURE
  SmsManager.RESULT_ERROR_NO_SERVICE
  SmsManager.RESULT_ERROR_NULL_PDU
  SmsManager.RESULT_ERROR_RADIO_OFF
  </code></pre>
  
  <p>What's meant by every one of them? and please mention a test case that could generate each one.
  I know that RESULT_OK denotes a successfully sent SMS. GENERIC_FAILURE occurs for general erros (e.g. I've no credit).</p>
  
  <p>But I've activated Airplane mode and tried to send an SMS. I've thought it would trigger NO_SERVICE error, but a RADIO_OFF was triggered instead. Also the official documentation is not demonstrating them very well.</p>