Reg Validation

I have 3 textboxes which will store homeph, cellph, workph,,
I need to set validation such that user must fill atleast one textbox.........i need to know how i could validate this....i don't want to have required validation on each of these textboxes
Here is my code
 
<tr>
            <td style="width: 153px">
                <asp:Label ID="Label9" runat="server" Style="position: relative; left: 35px; top: -1px;" Text="Home" Font-Bold="True" Font-Size="Medium"></asp:Label></td>
            <td style="width: 120px">
                <asp:TextBox ID="TextBo ...