If you want to dissable WSDL-caching, you can do so with
<?php
ini_set('soap.wsdl_cache_enabled', '0');
ini_set('soap.wsdl_cache_ttl', '0');
?>
However you must do this before creating a SOAP object (soap_client or soap_server).
Changing the settings like above does not have any effect on already existing soap-objects.
[EDIT BY danbrown AT php DOT net: Typofix provided by (james AT voodoo DOT co DOT uk) on 4-FEB-09.]