What preconditions need to be fulfilled for a SIP UA with third-party specific user identity to initiate a call flow?
Subscription data for verification of third-party specific user identity for the originating UE
Allocation of a designated Public User Identity by the HSS
Authorization of the third-party Authorization Server by the serving IMS network
Subscription data for allocation of Public User Identities for the terminating UE
Authorization of the SIP UA by the third-party Authorization Server