To assess the effectiveness of telephone-based interventions for mental illness, a systematic search of the literature was conducted using the databases PsycINFO and PubMed, and the search engine Google Scholar. The search identified 14 studies evaluating telephone-based interventions in the areas of depression (n = 6), anxiety (n = 3), eating disorders (n = 3), substance use (n = 1) and schizophrenia (n = 1). Although these studies provide evidence that telephone interventions can be effective, the few studies conducted, small sample sizes and lack of randomized controlled trial methodology prevent firm conclusions from being drawn. The articles reviewed suggest that an effective telephone intervention includes clearly structured therapy sessions and homework tasks. However, further evidence using large-scale, randomized controlled trials must be obtained in order to inform government and telephone counselling agencies about the efficacy of telephone interventions.