title: Two way SMS threads
body: <p>I am trying to write a threaded messaging application.</p>
  <p>Users can be in multiple threads and send/receive messages using SMS (probably with Nexmo or Twilio).</p>
  <p>How can I link an SMS reply to the original message? In e-mail we use a thread-&gt;id in the reply to.</p>
  <p>Not sure if this is even possible.</p>
  <p>Mick</p>