This paper presents descriptive accounts of time-critical organizing in the domain of emergency response. Patterns of mobile phone interaction in such work is analyzed showing how the dyadic exchange of mobile phone numbers between the actors plays an important role in the social interactions in the organizing and sensemaking of the emergency. Enacted sensemaking is used as an analytical framework. Implications for design of emergency response information technology are outlined and discussed. Author Keywords Ethnography, Enacted sensemaking, Mobile phones, Collaboration, Emergency Response ACM Classification Keywords H5 Information interfaces and presentation (e.g. HCI): H5.0 General, H.5.3 Group and Organization interfaces