Note that proxy_port value must be an integer. That seems obvious but problematic if you dynamically load application parameters as constants from a database.
$options = array( 'proxy_host' => PROXY_HOST,
'proxy_port' => intval(PROXY_PORT));
$client = new SoapClient( "some.wsdl", $options);
'proxy_port' => intval(PROXY_PORT));
$client = new SoapClient( "some.wsdl", $options);