Social networks and their applications have become extremely popular during the last years, mostly targeting users via the web. However, it has been recently observed an interest to offer social network services to mobile users. Telecom operators attempt to integrate existing social networks to their systems or develop new ones, in order to offer new services to their subscribers. Subsequently, emphasis is given to the user-context modeling, as well as to the integration of sources that leads to the summarized collection of information anchored to the user; such as its location or its mobile device type, etc. In this paper we discuss the most important factors and challenges encountered during the design of such a system on architectural, technological and tool level.