title: AT+CMGS returns ERROR
body: <p>I am using SIM900 GSM module connect to my AVR Microcontroller.
  I tested it with FT232 to see transmitting data.
  First Micro sends AT it will response OK</p>
  
  <pre><code>AT OK
  AT+CMGF=1 OK
  AT+CMGS="+9893XXXXXX" returns ERROR and doesn't show "&gt;"
  </code></pre>
  
  <p>Could anybody advise me what to do?</p>