title: asp.net validate textbox - at least one text box must have data in
body: <p>I have three textboxes and I want to validate them. At least one textbox must contain data.</p>
  
  <p>How can I do this?</p>
  
  <p>(The textboxes are Home Phone No., Work Phone No., Mobile No. and I need to check at least one method of contact is specified)</p>