. The information about the location of a mobile user belongs to the most sensitive data within mobile communication networks. One possibility to protect it especially against curious insiders with access to the network consists of storing the actual information in so-called "home trusted devices" and using temporary pseudonyms for user registration in the network databases. This paper presents a detailed OPNET simulation and evaluation of the signalling cost of this approach compared to standard GSM. 1 Introduction In contrast to previous mobile communication networks, GSM offers a much higher level of security to its users and the network operator, e.g. by authentication and speech encryption procedures as well as the use of temporary identities protecting the user's privacy. Despite these features, there are some security weaknesses in the GSM standard, e.g. the issue of protecting location information about the user (as it is contained within the GSM signalling information). The t..