This study designed learning activities supported by a mobile learning system for students to develop listening and speaking skills in English as a foreign language (EFL). How students perceive learning activities and a mobile learning system were examined in this study. Additionally, how different practices relate to students' language proficiency was also explored. It was found that students had positive perceptions and intentions toward learning activities; thus, students were motivated to practice English skills more when using a mobile learning system. The results demonstrated how students' speaking and listening skills practices using mobile devices had different correlations depending on their proficiency levels. For example, listening diversity, defined as the number of other classmates a student listened to, was found to have an inverse correlation with speaking and listening proficiency. This finding does not support previous research and indicates that students who carefully selected their listening partners performed better than those who did not. It was further found that the better students performed in English learning, the fewer partners they would choose. EFL instructors can use the insights of this study to design more effective language learning activities for students using mobile devices.