Advanced Mobile Phone Service.
The analog wireless transmission standard (technology) deployed in the 1980s in the United States. AMPS operates only in the Cellular frequency band (800 MHz).
AMPS networks are still operating, and offer excellent coverage of most of the country. Many current phones feature AMPS for analog roaming where digital service is not available.
AMPS uses more battery power and emits more radiation than digital modes. Digital modes also have generally better sound quality than AMPS, and provide more features.