[рони]

suxxoi,

$(function() {
    var phone = $("#phone")[0];
    $("#country_code").change(function() {
        var id_country = this.value;
        $.ajax({
            type: "POST",
            url: "/ajax/country.php",
            data: "id=" + id_country,
            dataType: "json",
            success: function(data) {
                var current = phone.value.replace(/.*(\d{9})$/, data.num+"$1");
                phone.value = current
            }
        })
    })
});