How can I display 3 buttons on a MessageBox?

I would like to show 3 buttons on a MessageBox. I 开发者_C百科found the Guide.BeginShowMessageBox method, but it isn't working with 3 buttons. Here is my code:

Guide.BeginShowMessageBox("Info", "This is a test messsage.",
        new List<string> { "OK", "Retry", "Cancel" }, 0, MessageBoxIcon.Warning,
        asyncResult =>
        {
            int? returned = Guide.EndShowMessageBox(asyncResult);
            Debug.WriteLine(returned.ToString());
        }, null);

Thanks, Laci

From MSDN:

The maximum number of buttons is two on Windows Phone, and three on Xbox 360 or Windows.

Are you on Windows Phone?