An emergency-use-only cellular phone provides for contacting and establishing full-duplex voice communication with emergency personnel at either a public emergency response service or a private roadside assistance service. The phone automatically places a cellular call to the public emergency response service with a single press of a first activation button, and to the private roadside assistance service with a single press of a second activation button. When either activation button is pressed, the following functions are initiated: (1) electrical power from a power supply is provided to a cellular transmitter and receiver, (2) the cellular receiver is activated to search for an available channel from among A or B cellular system channels, (3) an emergency telephone number corresponding to the selected service is accessed from memory, and (4) the cellular transmitter is activated to establish communication with the selected emergency response service. Since all of these functions are initiated by pressing one button, communication with the selected emergency response service may be established simply and speedily, even under stressful conditions. The phone may include a modular GPS receiver unit for providing location information to the public emergency response service or a private roadside assistance service.