Use arrays :
function test($options = array()) {
$defaults = array(
't1' => 'test1',
't2' => 'test2',
't3' => 'test3',
);
$options = array_merge($defauts, $options);
extract($options);
echo "$t1, $t2, $t3";
}
Call your function this way :
test(array('t3' => 'hi, i am different'));