On php|architect's A/R/T article repository today, there's a new tutorial from Paul Reinheimer covering the SOAP support that's built into usual installations of PHP5.
One of PHP5's landmark new features is the inclusion of a library of SOAP functions that make it easy to interact with SOAP based web services. While these functions are very powerful, learning to use them the first time can be a little intimidating. The goal of this article is to introduce you to PHP5's basic SOAP functions and how they are used through a working example.
The tutorial dosen't teach you about what SOAP is, so you'll need to find a different resource for that. If you've already added that to your ever-growing list of web protocols you know, then you'll feel right at home. For his examples, he uses the Amazon Web Services interface.
He jumps right in, defining a new SoapClient object for a remote resource, and shows how to display the WSDL results and make a call to the API based on the information it provides (in this case, a KeywordRequest call). He shows the response message this sample call will get, and brings the code pieces from the article together in a complete client to display them.