According to relevance theory (Sperber and Wilson, 1995), information (a set of assumptions in its terminology) is relevant if it satisfies two conditions; firstly, it should generate a substantial amount of interest (positive cognitive effects in its terminology); and secondly, its processing should demand as little mental effort as possible. In my opinion, this pair of conditions should be supplemented with the notions of contextual constraint and non-intended non-propositional effect.As will be argued in this paper, this RT extension is particularly appropriate for the analysis of Internet-mediated communication, since nowadays we are witnessing a turn into what has been labeled phatic Internet, massive exchanges of messages with little informational relevance but enormous impact on users' feelings of connectivity and sociability, among others. The aim of this paper is to apply this proposal of extension to mobile instant messaging (specifically WhatsApp) and explore some of the constraints and non-propositional effects that play a role in the eventual relevance of WhatsApp interactions, which typically generate relevance from these nonpropositional effects and not from the prototypical object of pragmatic research, namely the propositional content of the messages in the shape of explicatures and/or implicatures.