<?php

$arrItemList = array("regions"=>"array("IE,GB","BE,LU,GB","AU,NZ"));
/*$callback = function(''){

}*/

function callback($warr,$v) {
$warr = array_merge($warr,$explode(",",$v);
return $warr;
}

$arrCountrylistToFilter = array_reduce($arrItemList["regions"],callback);
print_r($arrCountrylistToFilter);

?>