A method for storing data in an IP multimedia subsystem (IMS) is disclosed. The method comprises: i) selecting a first user and a second user, which are not aliases; ii) analysing first and second data sets associated with the first and second users respectively to identify common data elements in each of the first and second data sets, the first and second datasets being useable by a first application server within the IMS to satisfy service requests on behalf of the first and second users; iii) creating a data structure containing a single instance of the identified common data elements; and iv) storing the data structure in a home subscriber server (HSS) within the IMS.
