Hello, i have a regex on my textfield, but i dont want only validade but show a mask on it

E.G
Phone Field
(XX) XXX-XXX

I'm validating by regex
<ext:TextField ID="txtTelResid" runat="server" FieldLabel="Tel. residencial" AllowBlank="true"
                                                        MaxLength="50" LabelCls="lblTab100" Cls="txt237" Regex="/\(\d{2}\)\ \d{4}\-\d{4}/"
                                                        RegexText="Telefone Inválido" ></ext:TextField>
but the user must type the ( ) for the phone, and i wants to show it automatically.
How can i do this

Thanks.