This paper explores the use of mobile technologies in facilitating offline encounters, through a post-digital lens which posits the digital not as new or disruptive but as a ubiquitous and accepted part of everyday social connectivities. In the paper, we explore ways in which migrants draw on jointly assembled semiotic repertoires, affordances, and constraints of the digital space, as well as cultural knowledge and spatial relating, to establish common ground and an interpretative framework for engaging in ensuing offline encounters. Drawing on an interactional analysis of data from a large linguistic ethnographic project, we focus on how a group of Polish immigrants who live in different parts of London bring their offline contexts and socially or culturally motivated expectations into their interactions to facilitate alignment in interactional frames in the context of limited familiarity with each other. Overall, our analysis points to the role of group messaging in creating a "digital prospection space" in which a joint frame of reference can be interactively constructed in anticipation of an offline encounter.