Here is an example of the method for creating a new type of enum:
$server->wsdl->addSimpleType('ServerStatus', 'xsd:string', 'SimpleType', 'struct',
array(
'Off',
'Stopped',
'Running'
));
Then, in Server structure the following line defines the server's status:
'Status' => array('name' => 'Status', 'type'=> 'tns:ServerStatus')
When web references are updated at client side, ServerStatus is translated to enum.