In 1992, the digital cellular standard GSM was introduced into several European countries. Based on this development, in conjunction with the deregulation of the telecommunications market, the substantial miniaturization of terminals, and the creation of new mass marketing strategies and user practices, the mobile telephone was transformed from an elite tool for businessmen into an everyday communication tool. Taking the case of (West) Germany, this article emphasizes the power of mobile telephone users in this transformative process. To evaluate the impact of mobile telephones, it proposes an heuristic which distinguishes between «prospective users» as they are constructed by planners, producers or marketing institutions, and «real users» who actually use the technology in their daily lives. While the idea of businessmen in need of a mobile office dominated GSM’s planning and early implementation phase, later developments took both system-builders and system-users by surprise. Through largely unforeseen practices, mass consumers shaped mobile telephony into an everyday technology used to master micro-mobility and social networking. The flexibility of the GSM standard enabled both creative re-interpretation of the technology and regular upgrades. Some of these upgrades, however, reflected marketing hopes rather than the actual practices of real users.