NuSOAP and PHP SOAP is designed as an XML wrapper for web services requests and responses. SOAP's strength lies in its use of namespaces, XML Schema datatypes, and its flexibility with regard to transports.
The disadvantage of SOAP is the fact that the specs and implementation is more complex, especially when you compare it to the simple XML-RPC approach. SOAP is the bread and butter of corporate web service developers. It has been deeply integrated into Microsoft .NET and IBM WebSphere. Based on its popularity, Google and Amazon.com have both created SOAP-based Web services.
NuSOAP is a powerful API developed for the PHP platform. It allows you to build both Web service clients and servers. One of the great features of NuSOAP is the built-in WSDL support.
Installing the API is a snap: all you need is a PHP enabled server. The required libraries are contained in a file called nusoap.php. You can download both the toolkit and the documentation at this link: http://deitrich.ganx4.com/nusoap/.