I want to provide an webservice server, written in SOAP.
Clients from other Hosts should get data from my SOAP server, but I canīt guarantee, that SOAP is installed at the client.
Is it possible to request a SOAP server with a "default shared webhosting" setup?
And if yes, what library makes this possible? XML_RPC perhaps?
First let's make this clear: SOAP is one thing, and XML-RPC is another thing.
Both allow you to provide webservices, but both work very differently.
Since you want to provide an webservice using SOAP. I'd advise you to use NuSOAP which is an excelent PHP toolkit to create your webservice server or client. If you search around the web for a way to create a server using NuSOAP, you'll find a whole range of examples from which you can learn