Mobile phones have recently been used to collect large-scale continuous data about human behavior. This people centric sensing paradigm is useful not only from a scientific point of view: Contextual user data has pragmatic value, too. Individuals whose data is collected in such long-term people centric sensing projects can be engaged in user centric design activities aiming to generate data driven services that benefit the end user. This paper demonstrates the value of such user centric approach. In a two-stage approach, we analyse mobile phone data to extract mobile phone usage categories. We then go on to interview the participants concerning their perceptions toward context- aware services. The two stages, combined as we present here, offer a clear value in terms of providing complementary insights, both to researchers and users, about the feasibility of and the expectations about personalized mobile services.