$proxy = new SoapClient('http://magentohost/api/soap/?wsdl');
$sessionId = $proxy->login('apiUser', 'apiKey');

$attributeToUpdate = array(
    "scope" => "global",
    "is_unique" => 1,
    "is_required" => 1,
    "is_configurable" => 1,
    "is_searchable" => 1,
    "is_visible_in_advanced_search" => 0,
    "used_in_product_listing" => 0,
    "additional_fields" => array(
        "is_filterable" => 1,
        "is_filterable_in_search" => 0,
        "position" => 2,
        "used_for_sort_by" => 0
    ),
    "frontend_label" => array(
        array(
            "store_id" => 0,
            "label" => "A Test Attribute"
        )
    )
);

$result = $proxy->call(
    $sessionId,
    "product_attribute.update",
    array(
        $attributeToUpdate
    )
);

<?php
//ini_set("soap.wsdl_cache_enabled", 0);

$client = new SoapClient('http://magentohost/api/v2_soap/?wsdl');

//V2
$session = $client->login('apiUser', 'apiKey');

// V2 WS-I Mode
//$response = $client->login(array('username' => 'apiUser', 'apiKey' => 'apiKey'));
//$session = $response->result;


//v2
$attributeCode = "code1";
$data = array(
   "frontend_input" => "text",
   "scope" => "1",
   "default_value" => "1",
   "is_unique" => 0,
   "is_required" => 0,
   "apply_to" => array("simple"),
   "is_configurable" => 0,
   "is_searchable" => 0,
   "is_visible_in_advanced_search" => 0,
   "is_comparable" => 0,
   "is_used_for_promo_rules" => 0,
   "is_visible_on_front" => 0,
   "used_in_product_listing" => 0,
   "additional_fields" => array(),
   "frontend_label" => array(array("store_id" => "0", "label" => "some random label updated"))
  );

$orders = $client->catalogProductAttributeUpdate($session, $attributeCode, $data); 



//V2 WSI
//WSDL WSI Sample is not complete
//$result = $client->catalogProductAttributeCreate(array("sessionId" => $session, "data" => $data));
//$orders = $result->result->complexObjectArray;

echo 'Number of results: ' . count($orders) . '<br/>';
var_dump ($orders);
?>