A method and apparatus for registering a user as a subscriber in a communication network. The method includes transmitting a registration message which defines an identity of the user to the communication network. The method also includes providing in the registration message a header field for defining at least one other identity of the user as a subscriber. The method also includes performing a one-by-one registration based on an identity information stored at a terminal device, whereby the identity information defines at least one other identity of the user as a subscriber. Thus, the user or subscriber can register some or all of his public identities at once with one registration procedure, allowing the user to utilize his identities by grouping public identities under user profiles or under private identities, while preventing unwanted calls.