$arr = array('141241241', '5463263', '124124124', '4254512');
if (in_array("$id", $arr)) {
    echo "Найден ID - ".$id."<br>";
}

RewriteEngine On
    RewriteBase /
    RewriteCond %{REQUEST_FILENAME} !-f
    RewriteCond %{REQUEST_FILENAME} !-d
    RewriteRule . /index.php [L]

<?php
    $url = explode('/',strtolower(substr($_SERVER['REQUEST_URI'], 1)));

    switch($url[0]) {
        case '': { 
            include 'pages/main.php';
            break;
        }
        case 'how_to_buy':{
            include 'pages/how_to_buy.php';
            break;
        }
        case 'payment_methods':{
            include 'pages/payment_methods.php';
            break;
        }
        case 'guarantees':{
            include 'pages/guarantees.php';
            break;
        }
        case 'payment':{
            include 'pages/payment.php';
            break;
        }
        case 'myorders':{
            include 'pages/myorders.php';
            break;
        }
    }
?>