title: C# phone number check
body: <p>I am doing validation for 10 digit North American phone numbers (coding below). I am accepting digits only. What I can't seem to figure out is how to alter this so that if the number entered begins with 911, 411 or a 0, an error is thrown. </p>
  
  <pre><code>string phoneNum = phoneTextBox.Text;
  Regex regex = new Regex(@"^\d{10}$");
  Match match = regex.Match(phoneNum);
  if (!match.Success)
  {
     MessageBox.Show(phoneNum + " is not a valid 10 digit phone number (Ex. 6134561234)");
  }
  </code></pre>