While existing literature supports the use of smartphones to teach English vocabulary, limited studies have addressed how learned words can be transferred to college students’ writing. This action research study designed pretest, treatment on mobile phones, posttest, and out-of-class pair-work, followed by a delayed posttest after three weeks to promote academic vocabulary use in writing. In the four-week treatment, academic words and collocations were designed using Quizlet units, combined with in-class writing practice. In the pair-work stage, the participants were allowed freedom to choose words they desired to learn and to exchange each other’s word logs with recycling of taught vocabulary designed in the treatment. Assessment of the pretest, posttest, and the delayed posttest involved (a) a general academic vocabulary test (receptive knowledge), (b) a vocabulary test of target words (gap-filling), and (c) an in-class writing task. Results show that our mobile-assisted language learning (MALL) project helped participants remember more words after their MALL experiences and apply them in their writing; meanwhile, such improvement could be maintained. Pair work was more favored than individual work as the participants indicated a stronger preference and endorsed collaborative learning. We argue that mobile devices should be combined with new learning strategies for both in-class and out-of-class learning.