Individuals experiencing homelessness have disproportionately high rates of health problems. Those who perceive themselves as having greater access to their social support networks have better physical and mental health outcomes as well as lower rates of victimization. Mobile phones offer a connection to others without the physical constraints of landlines and, therefore, may make communication (e.g., access to one's social support networks) more feasible for homeless individuals. This, in turn, could lead toward better health outcomes. This exploratory study examined mobile phone possession and use among a sample of 100 homeless men and women who do not use the shelter system in Philadelphia, PA. Interviews were comprised of the Homeless Supplement to the Diagnostic Interview Schedule, a technology module created for this investigation, and the substance use and psychiatric sections of the Addiction Severity Index. Almost half (44%) of the sample had a mobile phone. In the past 30 days, 100% of those with mobile phones placed or received a call, over half (61%) sent or received a text message, and one fifth (20%) accessed the Internet via their mobile phone. Participants possessed and used mobile phones to increase their sense of safety, responsibility (employment, stable housing, personal business, and sobriety or "clean time"), and social connectedness. Mobile phones could potentially be used by public health/health care providers to disseminate information to the street homeless, to enhance communication between the street homeless and providers, and to increase access for the street homeless to prevention, intervention, and aftercare services. Finally, this technology could also be used by researchers to collect data with this transient population.