Hi, there
The BPMN2 spec doesn't provide a node that represent exactly the same as the state node in jBPM3.
We probably provide an extension to the BPMN2 spec in order to support that functionality.
Right now in jBPM5 you can implement your Custom WorkItems (Service Task in the Spec), register it and inside it create an asynchronous interaction with your external service/application.
If you take a look at the documentation you will find how to create a new work item and how to plug it inside the eclipse palette.
http://downloads.jboss.com/drools/docs/5.1.1.34858.FINAL/drools-flow/html_single/index.html#ch.Domain_Specific_Processes
Greetings