A SUBSCRIBER SERVER SYSTEM FOR A CELLULAR COMMUNICATION SYSTEM

A subscriber server system 200 for a cellular communication system 100 comprises a subscriber data storage 205 which stores public identities associated with subscribers of the cellular communication system. A request processor 207 receives an identity information request message, such as a SIP OPTIONS message, from a remote station 101. The identity information request message comprises a first public identity for a subscriber of the cellular communication system. A public identity processor 209 determines a first set of public identities which comprises a plurality of public identities associated with the subscriber in response to the public identity. A message generator 211 generates an identity response message, such as a SIP 200OK message, comprising the first set of public identities. The identity response message is then transmitted to the first remote station 101.