According to Yahoo Biz, a company called WSO2 released their WSO2 WSF Framework C-library. What is more appealing is that there are now bindings for PHP available under a Apache 2.0 license. The company WSO2 describes itself as: "We are thought leaders in the Apache Web service project, where our engineers are core contributors to key projects including Apache Axis2, Apache Sandesha, Apache Rampart, Apache Neethi, Apache Axiom and Apache Synapse."
The framework provdes a set of resources that can be used to quickly create web services for your application. It also features interoperability with .NET and J2EE implementations.
The ThinkPHP post even helps you take the first steps by providing a step-by-step guide to installing the source and getting it up and running.