title: jQuery custom validation: phone number starting with 6
body: <p>I have a form in which you have to input your phone number and other fields. </p>
  
  <p>I'm validating the form with jQuery Validate. </p>
  
  <p>To validate the phone number field I do: </p>
  
  <pre><code>rules: {
      phone: {
      required: true,
          minlength: 9,
          number:true
      },..
  </code></pre>
  
  <p>But I need to check also that phone starts with 6. </p>
  
  <p>How can I do that? </p>