title: Receiving text messages with ZTE MF831 not working
body: <p>I got myself a ZTE MF831 modem to do some automations over text messages. I changed the mode to factory mode, so I can send instructions over <code>/dev/ttyUSB2 115200</code> (using screen or node with serialport).</p>
  
  <p><strong>Sending text messages works just fine.</strong> I receive the text on my personal phone. But when I send a message back (already sent several) I cannot read them. <strong>The folders on my modem are always empty.</strong> Even though I receive a notification like <code>+CMTI: ME,0</code>.</p>
  
  <p>These are the commands I send:</p>
  
  <pre><code>ATZ           -&gt; OK
  AT+CMGF=1     -&gt; OK
  AT+CPMS=?
    -&gt; +CPMS: ("ME","MT","SM","SR"),("ME","MT","SM","SR"),("ME","MT","SM","SR")
    -&gt; OK
  
  AT+CPMS="SM"  -&gt; +CPMS: 0,20,0,100,0,100
                -&gt; OK
  AT+CMGL="ALL" -&gt; OK
  
  AT+CPMS="ME"  -&gt; +CPMS: 0,100,0,100,0,100
                -&gt; OK
  AT+CMGL="ALL" -&gt; OK
  
  AT+CPMS="MT"  -&gt; +CPMS: 0,100,0,100,0,100
                -&gt; OK
  AT+CMGL="ALL" -&gt; OK
  
  AT+CPMS="SR"  -&gt; +CPMS: 0,100,0,100,0,100
                -&gt; OK
  AT+CMGL="ALL" -&gt; +CMS ERROR: 500
  </code></pre>
  
  <p>As you can see, there is always no text available. <strong>So I swapped my SIM card to another phone and tried again: I receive messages indeed.</strong></p>
  
  <p>What am I doing wrong?</p>