$front = array("front_first","front_second");
$inside = array("inside_first", "inside_second", "inside_third");
$back = array("back_first", "back_second", "back_third","back_fourth");
function foo() {
$args = func_get_args();
$max = max(array_map('sizeof', $args)); // credits to hakre ;)
$result = array();
for ($i = 0; $i < $max; $i += 1) {
foreach ($args as $arg) {
$result[] = isset($arg[$i]) ? $arg[$i] : end($arg);
}
}
return $result;
}
$final = foo($back, $front, $inside);
print_r($final);
demo: http://codepad.viper-7.com/RFmGYW