The style for a
SOAP message can be RPC or Document, not sure where Message style comes in.
RPC means that the body of the SOAP message represents a Remote Procedure Call, with procedure name and in and out parameters - i.e. think of it as invoking a method provided by the webservice.
Document means that the body of the SOAP message is an XML document to be sent to the service, the document could still be thought of as the parameter to a procedure call, but its more flexible in what is sent and how its interperated by the web service.
Not a speedy response, but since no one else has replied I thought I'd have a go, note that this is just my understanding - feel free to correct me if its wrong