Something i found useful for talking to a SOAP web service running in a windows server 2003 is ASIHTTP (
pokeb's asi-http-request at master — GitHub), i had to compose the xml query myself using TouchXML and parse the response with NSXMLParser.
Also got some great response from ASIHTTP's developer to adapt it for SOAP webservice, it also has authentification and progress state support.
In the end i got a good way of sending program objects to the SOAP service an getting objects back (something that should already be included in the SDK IMHO).
