kseosru,
<!DOCTYPE html>
<html>
<head>
<title>Untitled</title>
<meta charset="utf-8">
<style type="text/css">
.hide{
display: none;
}
</style>
<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.12.4/jquery.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery.maskedinput/1.4.1/jquery.maskedinput.min.js"></script>
</head>
<body>
<select id="country" class="form-control">
<option value="ru">
Россия +7
</option>
<option value="ua">
Украина +380
</option>
<option value="by">
Белоруссия +375
</option>
</select> <input id="phone" placeholder="Введите 16 цифр" type="text" class=
"form-control">
<script>
jQuery (function ($) {
$(function() {
function showDiv()
{
$('.hide').toggle($("#phone").val().replace(/\D/g, '').length === 16)
}
function maskPhone() {
var country = $('#country option:selected').val();
switch (country) {
case "ru":
$("#phone").mask("9999 9999 9999 9999", {
completed : showDiv}).on('keydown.mask',showDiv);
break;
}
}
maskPhone();
$('#country').change(function() {
maskPhone();
});
});
});
</script>
<div class="hide">
Появление DIV (скрытый )
</div>
</body>
</html>