Previous studies have shown diverse applications of technologies to facilitate language learning, and positive adoption of flipped instruction over conventional approaches. They have affirmed the Technology Acceptance Model (TAM) as a dominant model in exploring the perceptions of learners about technological acceptance. Nevertheless, research in light of TAM into mobile-based flipped learning among learners of different proficiency levels in an EFL setting remains scarce. This study therefore performed critical analysis of the dynamics embedded in EFL learners' technological acceptance. The participants were 42 sophomore English-majors taking English Oral Training classes. A mixed method was employed to analyze multiple sources of data, including pre- and post-tests of oral proficiency, the TAM questionnaire, and semi-structured focus-group interviews. The results revealed positive effects of the mobile-based flipped instruction over the conventional lecture-based approach, and yielded the determinant role of attitude about the use of LINE in learners’ subsequent behavioral intention to accept the integration of such technology in language learning, albeit differences in the construct relationship among students of difference proficiency levels. The authors present insights into factors affecting EFL learner acceptance of a chosen technology, perceptions of flipped learning experience, and pedagogical recommendations for future practice.