On the PHP::Impact blog Federico offers a brief tutorial on creating a simple web service client with the help of the Zend Framework.

The Zend Framework puts heavy emphasis on Web services. This is a good thing, considering the amount of Web services out there that can help lower costs and increase the value of your site. [...] In this example, I'll develop a Web services client to Digg, a real-world Web services provider.

He steps through the process - finding the provider information, locating their endpoints, setting up query string interfaces, making code to handle the responses and, finally, making the actual client as a Zend_Rest_Client interface.