javascript validation to enter landno(eg:040-123456)

<script type="text/javascript">

function NumericTextBox(evt)
{
  
    var charCode = evt.keyCode;
   
        if(evt.ctrlKey == true)
        {
        if(charCode == 67 || charCode == 86)
        {
         return true;
        }
        }
        if (charCode == 8 || //backspace
                charCode == 46 || //delete
                charCode == 13 || //enter key
                                charCode == 189)   //hipen key
    {
        return true;
    }
    else if (charCode >= 37 && charCode <= 40) //arrow keys
    {
        return true;
    }
       
    else if (charCode >= 48 && charCode <= 57) //0-9 on key pad
    {
        if (evt.shiftKey == true)
            return false;

        return true;
    }
    else if (charCode >= 96 && charCode <= 105) //0-9 on num pad
    {
        if (evt.shiftKey == true)
            return false;

        return true;
    }
    else
        return false;
}

    </script>



<asp:TextBox ID="txtMobile" runat="server" size="50" onkeydown="return NumericTextBox(event);"
                                ToolTip="Enter Mobile No" MaxLength="16"></asp:TextBox>