This study explored how four groups of language learners used a mobile software application developed by the researcher for learning idiomatic expressions and collocations. A total of 45 participants in the study used the application for a period of one week. Data for this study was collected from the application, a questionnaire, and follow-up interviews. Findings show that participants usage of the application correlated with their average scores on the quizzes in the application. The more participants used the application, the higher they scored on the quizzes which was the most used feature of the application. Findings show that usage of the application can be predicted by a variety of factors, such as language proficiency, users' average daily usage of their mobile devices, and motivation and learning goals. Findings also underscore the importance of providing language learners with resources to help them learn idiomatic expressions and collocation. Participants strongly indicated that even within a short period of time, they felt they know more idioms and collocations since they started using the application. Findings also show that participants' have strong positive attitudes toward the use of mobile technology in language learning.