Abstract: A method of reassigning user data in a communications system is disclosed, with a plurality of identities for each user. The method includes storing in a user information store the plurality of identities in association with a first serving controller, the plurality of identities being associated with respective registration statuses selected from a registered status and an unregistered status; detecting that the user has requested registration to a second serving controller using one of the identities; and issuing a registration termination request identifying each identity, which has been newly assigned to the second serving controller as a result of the requested registration. Responsive to the registration termination request, re-registration notification is issued to the user and all identities of the said user from the first serving controller are dissociated.

Abstract: A method of registering users in a mobile communications system, the method comprising the steps of: storing in a user information store primary and secondary identifiers identifying a first serving controller; receiving a request from a serving controller, said request identifying that serving controller using primary and secondary identifiers; comparing the primary identifier in the user information store with the primary identifier in said request and, if there is a mismatch, comparing the secondary identifier in the user information store with the secondary identifier in said request wherein, when there is a mismatch between the secondary identifiers it is determined that the serving controller identified in the request is not the first serving controller; and when there is a match between the secondary identifiers it is determined that the serving controller identified in the request is the first serving controller.