Putting SOAP service on PHP platform is a piece of cake. There are few nice articles out there that will pretty much guide you through the whole setup(which is in fact just putting together WSDL and server-side functions to handle a request), so after half an hour of messing around you can have your own SOAP thingie going. One draw back there – the article would get you as far as sending simple types(like strings and floats) back and force between client and server. Now, this isn’t very helpful if you’re trying to build something more object oriented.
The basic problem that I hit setting up SOAP server for a data-sharing application(pretty much content repository for a network of websites) – how to set up a custom complex data type without going through that whole WSDL spec?