MaskedEditExtender number only, remove trailing zeros?

I have the following ASP.NET code -

<asp:TextBox ID="txtCellPhoneNo" runat="server"></asp:TextBox><cc1:MaskedEditExtender ID="MaskedEditExtender1" runat="server"
    TargetControlID="txtCellPhoneNo"
    Mask="999-999-9999"
    MessageValidatorTip="true"
    OnFocusCssClass="MaskedEditFocus"
    OnInvalidCssClass="MaskedEditError"
    MaskType="Number"
    InputDirection="LeftToRight"

    ErrorTooltipEnabled="True" ClearMaskOnLostFocus="False" ClearTextOnInvalid="True"/>

When I type in "156" and tab out, it displays "156-000-0000". How do I get it to display only "156"? i want to display156-__-____

Thank you.