The rapid diffusion of communication technology has provided opportunities to enhance the delivery of mental health care. We used Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines to conduct a qualitative review of randomized controlled trials that reported on the efficacy of mobile phones or handheld computers used to enhance the treatment of psychiatric disorders. We identified eight randomized controlled trials. Five studies used mobile phones to target smoking cessation. Those receiving the smoking cessation intervention were significantly more likely to achieve abstinence compared with those under the control condition. Three studies used non-personal digital assistant (PDA) handheld computers targeting anxiety. Compared with those in the control condition, those who received the non-PDA handheld computer intervention had significant improvement in anxiety outcomes in only one of the three studies. The limited number of rigorous evaluations of mobile phone, PDA, or smartphone interventions for mental health problems underscores the opportunities to enhance our interventions using the available tools of contemporary technology.