title: How to add voice call feature to facebook page from messenger
body: <p>I am currently developing a facebook messenger bot.</p>
  
  <p>There is one feature that I want to add to my bot--voice call.</p>
  
  <p>Is there a way to allow users to call my page when I update the phone number on my app page?</p>
  
  <p>Best case would be putting calling button in menu or upper right corner where setting button is at. </p>
  
  <p>Thank you in advance.</p>