Motivation has long been recognized as a critical component of language learners' success. According to Self-Determination Theory (SDT), an autonomously motivated student is more likely to be engaged in a learning activity. As the learners' needs for autonomy, competence, and relatedness ought to be accommodated, these basic psychological needs of learners (BPNs) must be addressed to sustain autonomous motivation. Although there is a substantial number of literature that addresses the role of these three components in the context of mobile-assisted language learning (MALL) and their relationship to autonomous motivation (Kohnke, 2020; Alamer, 2021b; Kartal, 2019; Ali, 2019), the use of Microsoft Teams is almost never addressed. This study aimed to examine the relationship between the informal use of mobile apps by teachers, such as messaging applications, and their students' levels of motivation. This study involved one group of students divided into six sections with the same level of proficiency, who were enrolled in a foundation course in English at a private university in the United Arab Emirates (N = 344). The students were studied over a period of time (Phase 1 and Phase 2 groups of the same population). The analyses were carried out by the use of ANOVA with repeated measures and a t-test. Participants' autonomy and competence were found to have increased slightly as a result of the study. The study, however, failed to demonstrate any significant impacts on anxiety, self-confidence, engagement with language tasks, nor on actual achievement.