title: String.Format is not formatting phone number
body: <pre><code>String.Format("{0:###-###-####}", customer.ContactHome); //NOT working (9891205789)
  </code></pre>
  
  <p><strong>BUT</strong></p>
  
  <pre><code>String.Format("{0:###-###-####}", Convert.ToInt64(customer.ContactHome)); //Works fine (989-120-5789)
  </code></pre>
  
  <p>but I don't want to Cast phone no due to some reason. How can I format phone no without casting?</p>