function validate_callback ( )
{
    valid = true;
	
	
   if (( document.callbackform.contact_name.value == "" ) || ( document.callbackform.contact_name.value == "contact name" ))
    {
        alert ( "ERROR!\n\Please enter a contact name before continuing." );
        valid = false;
	}
  
   else if (( document.callbackform.contact_number.value == "" ) ||( document.callbackform.contact_number.value == "contact number" ))
    {
        alert ( "ERROR!\n\Please enter an telephone number before continuing." );
        valid = false;
	}
	
	   else if ( document.callbackform.time.value == "" )
    {
        alert ( "ERROR!\n\Please select a prefered contact time." );
        valid = false;
	}
	
    return valid;
}