Entering search terms on mobile phones is a time consuming and cumbersome task. In this paper, we explore the usage patterns of query entry interfaces that display suggestions. Our primary goal is to build a usage model of query suggestions in order to provide user interface guidelines for mobile text prediction interfaces. We find that users who were asked to enter queries on a search interface with query suggestions rated their workload lower and their enjoyment higher. They also saved, on average, approximately half of the key presses compared to users who were not shown suggestions, despite no associated decrease in time to enter a query. Surprisingly, users also accepted suggestions when the process of doing so resulted in an increase in the number of total key presses. Author Keywords Mobile search, text entry, query prediction. ACM Classification Keywords H5.2. Information interfaces and presentation: User Interfaces.