For 2015, and expected in future years, Jamboree on the Air station registration will be handled by the World JOTA-JOTI Team working with the World Organization of the Scout Movement.
Registration of your station can be accomplished at http://www.world-jotajoti.info/sign-up-for-jota-joti/
The list of world-wide registered stations can be found at http://jotajoti.info/registered-stations/