I am attending a course on WCF (Windows Communication Foundation).
State full services are sometimes not considered 'right' when speaking of Service Oriented Architecture (SOA).
My claim is that state has nothing to do with whether a service can be a good entity in a SOA architecture. You might have a strategy that your services should bee RESTfull, but that has nothing to do with whether your architecture is service oriented or not. REST gives you some other properties (quite useful I might add), but doesn’t influence the architecture towards SOA.
The same goes for callbacks. Even though my telephone company allows people to call me on my phone, I still consider my phone connection to be a service provided to me by my phone company.