function displayWindow(url, width, height) {
      var Win = window.open(url,"displayWindow",'width=' + width + ',height=' + height + ',resizable=1,scrollbars=1,menubar=no' );
}

function checkForm() {
    phone = document.getElementById('phone');
    mail = document.getElementById('mail');

    if (phone.value.length == 0 || mail.value.length == 0) {
        alert("Pola oznaczone * muszą zostać wypełnione.  ");
        return false;
    } else {
        return true;
    }
}