A generic method is described for storing data in the HSS (2) by the S-CSCF (1) of an IMS. When a SIP message containing new information relating to an IMPI/IMPU pair is received by the S-CSCF (1), a data package is created for storage at the HSS (2), containing the new information. An SAR command is sent to the HSS (2) containing an AVP including an instruction to the HSS (2) and the new data package. In one aspect a unique data package is controlled by the S-CSCF (1). When new information relating to the IMPI/IMPU is received in a SIP message, this is added to any previously sent data package to create a new data package. In another aspect the HSS (2) controls a unique data package, returning the data package to the S-CSCF (1) to be amended if necessary. In another aspect separate data packages are used.