SoapFault exception

I am new to PHP and web services, so this may be a simple nothing to some of you, but I would really appreciate the help.
What am I doing wrong in this script?


<?php
ini_set('display_errors','1');
error_reporting (E_ALL);

$GetUserName = new SoapClient("http://idm.east.dev.cox.net/idmwebservices/CoxIdentityServices?wsdl");

$account = array("GetAllAccountInfoAcctNbr" => "6111027582601");
$username_r = $GetUserName->username($account); <= line 11
$userId_r = $GetUserName->userId($account);

echo "<br>Account: $account";
echo "<br>User Name: $username_r";
echo "<br>User ID: $userId_r";

?>


Here is the message:

Fatal error: Uncaught SoapFault exception: [Client] Function ("username") is not a valid method for this service in /www/zendcore/htdocs/cox/GetAccountInfo.php:11 Stack trace: #0 [internal function]: SoapClient->__call('username', Array) #1 /www/zendcore/htdocs/cox/GetAccountInfo.php(11): SoapClient->username(Array) #2 {main} thrown in /www/zendcore/htdocs/cox/GetAccountInfo.php on line 11

The error is straightforward - $GetUserName->username() is not defined. Consult the API documentation to for the correct function to use.