define( 'UA_ALL', '/^([a-z0-9]+\/[\d.]+) \(([a-z; ]+)\) ([a-z0-9\/+]+) (\([a-z, ]+\))? (([a-z0-9\/.]+ ?)+)/i' );
    preg_match( UA_ALL, 'Mozilla/5.0 (iPhone; U; CPU like Mac OS X; en) AppleWebKit/420+ (KHTML, like Gecko) Version/3.0 Mobile/1A543a Safari/419.3', $matches );
    print_r( $matches );

Array
(
    [0] => Mozilla/5.0 (iPhone; U; CPU like Mac OS X; en) AppleWebKit/420+ (KHTML, like Gecko) Version/3.0 Mobile/1A543a Safari/419.3
    [1] => Mozilla/5.0
    [2] => iPhone; U; CPU like Mac OS X; en
    [3] => AppleWebKit/420+
    [4] => (KHTML, like Gecko)
    [5] => Version/3.0 Mobile/1A543a Safari/419.3
    [6] => Safari/419.3
)