<form action="" method="post" onsubmit="if(this.name.value==''){alert('Введите Ваше имя!');return
false}if(this.phone.value==''){alert('Введите Ваш номер телефона!');return false}urlGen(this);return true;">
<input type="hidden" name="product_id" value="PRODUCT_ID"/>
<input type="hidden" name="ref" value="WEBMASTER_ID"/>
<input placeholder="ФИО" maxlength="25" name="name" type="text">
<input placeholder="Телефон" maxlength="25" name="phone" type="text">
<button type="submit">Заказать!</button>
</form>