The difference between analog and digital technology is how the messages are transmitted and the sound quality of those voice transmissions. Analog technology uses a system called Advanced Mobile Phone Service (AMPS). AMPS uses analog radio frequency modulation (FM) for voice transmission. Digital technology uses one of the following systems: CDMA, TDMA, or GSM. In general, digital transmissions provide for highly private conversations with superior sound quality to analog transmissions. All major cellular phone carriers have advanced their systems to operate from a form of digital technology.