Mobile learning has long been identified as one of the natural directions in which CALL is expected to move, and as smaller portable technologies become less expensive, lighter and more powerful, they have the potential to become a more integral part of language learning courses as opposed to the more supplemental role often assigned to computer labs. Mobile phones have been the topic of a number of recent studies, including for learning pragmatic phrases via mobile email, and as electronic flash cards. With the development of mobile systems that can access the Internet, more sophisticated applications which allow the use of databases and interactive web content have been made possible. The current study describes one such application, investigating the use of a prototype mobile-based intelligent vocabulary tutor system by learners in an advanced EFL class. Learners used the tutor to complete vocabulary activities in a variety of task formats through either their mobile phone or through a computer, and the system kept logs of all access to the system. A profile of each learner was created in terms of the vocabulary that they had difficulty with, and presented these items to the learners more frequently than items that were less likely to cause learners problems. Learner access logs to the vocabulary activities and the learner profiles were analysed, and a survey was administered to learners at the completion of the project. The results are discussed in terms of learner usage patterns and learner perspectives regarding each platform.