how to display textbox , when radio button selected

<asp:Radiobuttonlist id="RadioButtonList1" runat="server" repeatdirection="Horizontal" autopostback="True" onselectedindexchanged="RadioButtonList1_SelectedIndexChanged" xmlns:asp="#unknown">
             <asp:listitem enabled="true" value="Airtel">Airtel</asp:listitem>
             <asp:listitem enabled="true" value="IDEA">IDEA</asp:listitem>
             <asp:listitem enabled="true" value="Docomo">Docomo</asp:listitem>
             <asp:listitem enabled="true" value="Other">Other</asp:listitem></asp:Radiobuttonlist>

protected void RadioButtonList1_SelectedIndexChanged(object sender, EventArgs e)
        {
            if (string.Equals(RadioButtonList1.SelectedValue,"Other"))
            {
               TextBox1.Visible = true;

            }
            else
            {
              TextBox1.Visible =false;
            }
        }