Interruption management in technology mediated communication is a key concern in ollaborative work and social environments. Previous empirical and theoretical work in predicting interruptibility predominantly focuses on interruptee's local context namely identifying cognitively and socially intruding contexts such as mental work load levels, activity, place of activity. They largely ignore the relational context namely "who" the interruption is from or "what" it is about. This paper addresses this issue by systematically investigating the use of the various contextual factors in interruption management practices of everyday cell phone use. Analysis of 1201 incoming calls from our experience sampling method study of cell phone use, shows that "who" is calling is used most of the time (87.4%) by individuals to make deliberate call handling decisions (N=834), in contrast to the inter ruptee's current local social (34.9%) or cognitive (43%) contexts. We present implications of these findings for the design of interruption management tools for communication media.