Although location-based reminder applications have been widely prototyped, there are few results regarding their impact on people: how are they used, do they change people’s behavior and what features influence usefulness the most. Cell phones provide a compelling platform for the delivery of location-based reminders within a user's everyday natural context. We present requirements for location-based reminders resulting from a qualitative study performed at small area in the city, and elaborate how these results are influencing ongoing design of a more comprehensive location-based reminder system. In this paper we propose an architecture of location based services which uses GPS. Within the architecture, we discuss the challenges for context management, service trigger mechanism and preference-based services.