In this paper, we demonstrate how ethnographic fieldwork studies can be used to inform the design of third generation mobile phones. We draw on a field study of teenage mobile phone users and, specifically, their participation in gift-giving practices to design the user interface and form of a concept mobile phone. The concept device is designed to support teenagers' social practices through a novel multimedia messaging system and the augmentation of the phone's address book. We report on the process adopted to design the concept and briefly describe preliminary reactions from potential users. To conclude the paper, we comment on the lessons we have learnt in applying ethnographic findings to design.