Treatment of user identities in the IP Multimedia Subsystem

Method of treatment of SIP requests received by a Network IP Multimedia Subsystem, the method characterized by: determining one of an I-CSCF, an S-CSCF, an HSS or SLF, if the identity of SIP destination of the request is or within a range of identities having an operator network but it is not currently assigned to a subscriber or network service comparing the identity of SIP destination identity data SIP destination unassigned and if so , route the message to one or more SIP application servers within the network and implement service logic in (the) server (s) specific application (s) of a SIP identity owned by the network but not assigned.