AMPS

AMPS stands for Advanced Mobile Phone System.  It was really the first entrance of cellular itself, and it was, is, an analog system (non-digital).  AMPs was widely used in the US before digital cellular systems such as iDEN (Nextel), GSM, TDMA and CDMA arrived.  AMPs was really very similar to FM radio - in that each cellular phone conversation was briefly allotted their own frequency for their own conversation that was different from other cellular conversation frequencies nearby.