The study aims at portraying EFL learners' interactivity and motivational dynamics when engaged in team-based mobile learning (TBML) through WhatsApp within the environment of English for Academic Purposes. Data were collected through survey on online learning engagement and learning motivation and analyzed using descriptive statistics coupled with correlation analysis. Thematic analysis was operative to analyze students' reflection for more fine-grained insights on the nature of collaborative mobile learning, supported with directed content analysis geared to Activity Theory (AT) on the archives of group's online discussion. Albeit technical challenges and negative affectivity therefrom, the findings emphasize the potency of WhatsApp as a social-network (SN) learning platform which engages language learners in supportive micro and macro learning environment as the pre-cursor to elevated motivation, self-regulation, and pedagogical rethinking. The implication highlights teacher's necessity to scaffold group dynamics and condition student's mentality to live the target language in the mobile learning.