There are provided mechanisms for registering and subsequently communicating with classified subscribers in an IMS environment. The method comprises replacing an IMS Public -and Private User identity (IMPU/IMPI) with randomized temporary identifiers. Parties, in particular parties with 5 access to network entities outside the home-network cannot relate the observed IMPU/IMPI to the subscriber's original IMPU/IMPI as provisioned, and as the temporary IMPU changes frequently, there is no pattern (registration nor call) to be allocated to the subscriber's UE.