DateTimeZone::listIdentifiers

It  returns numerically index array with all timezone identifiers
Example

<?php
$timezone_identifiers = DateTimeZone::listIdentifiers();
for ($i=0; $i < 10; $i++)
echo $timezone_identifiers[$i].”<br />”;

?>

Output

Africa/Abidjan
Africa/Accra
Africa/Addis_Ababa
Africa/Algiers
Africa/Asmara
Africa/Bamako
Africa/Bangui
Africa/Banjul
Africa/Bissau
Africa/Blantyre