This study examined how Korean teacher candidates' understanding of English and their use of the L2 (second language) and other semiotic resources for meaning making could be mediated through a mobile application, Band during study abroad. Drawing on the sociocultural perspective of L2 learning, the teacher candidates' weekly reflections, which were composed in L2 English along with other semiotic resources (e.g., emoticons, images, and videos) on curricular activities were analyzed and triangulated with focus group and individual interviews. Content analysis of the reflection posts indicated how the mobility and connectivity of Band mediated sojourners' understanding of variation in English and the host culture during study abroad. The analysis further suggests that the interactive and multimodal features of the mobile application helped L2 learners engage in enhanced learning opportunities through which they shared and negotiated each other's ideas, by using the L2 and other semiotic meaning-making resources, such as images and videos.