Mobile phone ownership among university students in Vietnam has reached almost 100%, exceeding that of Internet-capable desktop computers. This has made them increasingly popular to allow learners to carry out learning activities outside of the classroom, but some studies have suggested that learners are not always willing to engage in activities outside of the classroom (Kim et al., 2013). Recent research has suggested that providing training to learners that includes not only how but also why activities are important can improve learner engagement in mobile-based activities (Stockwell & Hubbard, 2014). In this presentation, Vietnamese learners of English engaged in vocabulary and grammar tasks using the Quizlet app on their mobile phones outside of class time. Learners were provided with technical training in class, while ongoing strategic and pedagogical training were provided through a combination of in-class activities and interactions through a dedicated Facebook page over a 5-week period. Usage patterns of the site were recorded through a learning journal and interactions on the Facebook page were analysed to determine the nature of the discussions that took place. Learner attitudes towards the tasks and the training were examined through pre- and post-questionnaires and a focus group discussion. The results are discussed in terms of the problems encountered, and some suggestions for providing appropriate training to learning through mobile phones outside of class through social networking.