This is an issue with the installation: please double check you don't have jbossws-native-* libs in your AS installation (including lib/endorsed dir).
As you say, JBossWS-CXF is not meant to use any org.jboss.ws.core.soap classes, hence the reason for it to search them stands in a wrong service file (coming from a jbossws-native lib) setting that factory.
Thanks for the info.
However, I checked the lib/endorsed and other library folders in my server instance and found no jbossws-native-*.
Just remembered that jboss 4.2.3 had jboss-saaj.jar too (that has been renamed to jbossws-native-saaj.jar later), try looking for that too (which might not have been removed by the jbossws-cxf install script).
It works after removing the jboss-saaj.jar from lib/endorsed folder.
Thanks you very much.