JBoss-WS4EE relied on a deprecated attachments technology called SwA (SOAP with Attachments). SwA required soap/encoding which is disallowed by the WS-I Basic Profile. JBossWS provides support for WS-I AP 1.0, and MTOM instead. There will be no API change for users, however, since this is an updated protocol you will not be able to transfer attachments between older versions of JBoss AS and JBoss AS 4.0.4 or above.

WS-I Attachment Profile 1.0 defines mechanism to reference MIME attachment parts using swaRef. In this mechanism the content of XML element of type wsi:swaRef is sent as MIME attachment and the element inside SOAP Body holds the reference to this attachment in the CID URI scheme as defined by RFC 2111.