$(document).ready(function () {
    $("input[name=callback]").click(function () {
        changePhone();
    });

    changePhone();
});

function changePhone()
{
    var isyes = $("input[name=callback][value=yes]:checked").length;

    if (isyes)
        $("#phoneholder, #timetocallholder").show();
    else
        $("#phoneholder, #timetocallholder").hide();
}