<?php

class timer {
    private $start_time = NULL;
    private $end_time = NULL;

    private function getmicrotime() {
      list($usec, $sec) = explode(" ", microtime());
      return ((float)$usec + (float)$sec);
    }

    function start() {
      $this->start_time = $this->getmicrotime();
    }

    function stop() {
      $this->end_time = $this->getmicrotime();
    }

    function result() {
        if (is_null($this->start_time)) {
            exit('Timer: start method not called !');
            return false;
        }
        elseif (is_null($this->end_time)) {
            exit('Timer: stop method not called !');
            return false;
        }

        return round(($this->end_time - $this->start_time), 4);
    }

}

function genRand($length = 10, $chars = '0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ') {
    $randomString = '';
    for ($i = 0; $i < $length; $i++) {
        $randomString .= $chars[rand(0, strlen($chars) - 1)];
    }
    return $randomString;
}

function populate($count = 10000) {
        $array = array();
        for($i = 0; $i < $count; $i++) {
                $phone = genRand(5,'0123456789');
                $array[$phone] = array(
                        'phone' => $phone,
                        'name' => genRand(20),
                        'age' => genRand(2, '0123456789'),
                );
        }
        return $array;
}

$array1 = populate(40000);
$array2 = populate(40000);

$match = FALSE;

$timer = new timer();

$timer->start();

foreach($array1 as $key => $value) {
    if(array_key_exists($key, $array2)) {
        $match = TRUE;
        break;
    }
}

$timer->stop();

print_r('Match '.($match ? '' : 'not')." found\n");

// show result now
print_r('For Each completed in '.$timer->result()."\n");

$timer = new timer();

$timer->start();

$matched = array_intersect_key($array1, $array2);

$timer->stop();

// show result now
print_r('Intersect Key completed in '.$timer->result()."\n"); // At least 100x longer...