Much of the literature theorising mobile learning emphasises the importance of context with physical and social contexts identified to date. Our work to design and implement authentic mobile simulation activities using SMS text messaging suggests that a third context may also be important. This is a virtual context, the learner-created cognitive space within which the activity takes place. The arrival of a message during a simulation activity will disrupt the real world physical and social contexts in which the learner finds themselves and transfer them into the virtual context. We argue that this disruptive power of the mobile device to shift the user's presence may be one of the distinguishing characteristics of certain mobile learning applications. This paper will explore the idea of the virtual context and discuss the role of issues of context, presence and disruption, illustrating these with reference to a case study of mobile simulation learning using SMS text messaging. (Contains 2 figures.)