According to relevance theory (Sperber and Wilson, 1995), information is relevant if it satisfies two conditions: it should produce a considerable amount of interest and its processing should demand as little mental effort as possible. It is argued that these conditions ought to be repleted with the concepts of contextual constraint and non-intended non-propositional effect. This RT extension is especially fit for the assay of Internet-mediated communication, as nowadays we are observing a turn into what has been tagged phatic Internet, huge message exchanges with little informational pertinence but vast influence on users’ feelings of connectivity and sociability, among others. This article sets out to apply this extension proposal to mobile instant messaging (specifically WhatsApp) and examine some of the constraints and non-propositional effects that play a role in the potential relevance of WhatsApp interactions, which typically produce relevance from these non-propositional effects and not from the prototypical object of pragmatic research, to wit the propositional content of the messages in the shape of explicatures and/or implicatures.