People with serious mental illness have changes in their condition that are hard to measure and lead to more care. It's unclear if speech can be used to track these changes. This study looks at whether speech samples can be collected from people with mental illness and used to track changes in their condition over time. 47 patients with bipolar disorder, major depressive disorder, schizophrenia, or schizoaffective disorder used a voice response system for at least 4 months to provide speech samples. Providers reviewed the responses and rated them. The study found that the system was easy to use and that individually-trained models had the highest correlation with provider ratings. Population-level models also showed correlations with some provider ratings and mental health scores. This study shows that speech can be used to track mental health in a community-based setting.