Magento: How to get customer session in external file.

Customer Session :

<?php
// Include Magento application
require_once ( "app/Mage.php" );//path to your magento Mage.php file
umask(0);

// Initialize Magento
Mage::app();

// You have two options here,
// "frontend" for frontend session or "adminhtml" for admin session
Mage::getSingleton("core/session", array("name" => "frontend"));

$session = Mage::getSingleton("customer/session");

if($session->isLoggedIn())
{
    echo "Logged in";
}else{
    echo "Not logged in";
}

Magento Session from external page (same domain)

<?php
require_once ('app/Mage.php');
Mage::app(); 

// Define the path to the root of Magento installation.
define('ROOT', Mage::getBaseUrl(Mage_Core_Model_Store::URL_TYPE_WEB));

// Obtain the general session and search for an item called 'customer_id'
$coreSession = Mage::getSingleton('core/session', array('name' => 'frontend'));
if(isset($coreSession['visitor_data']['customer_id'])){
    $customerId = $coreSession['visitor_data']['customer_id'];
} else {
    header('Location: '.ROOT.'customer/account/login/');
}

// Load the user session.
Mage::getSingleton('customer/session')->loginById($customerId);
$customerSession = Mage::getSingleton("customer/session");

// We verified that created successfully (not required)
if(!$customerSession->isLoggedIn()) {
    header('Location: '.ROOT.'customer/account/login/');
}

// Load customer
$customer = $customerSession->getCustomer();

// We get cell phone
$telefono = $customer->getTelefonoMovil();
?>