IS-54 and IS-136 are second-generation (2G) mobile phone systems, known as Digital AMPS (D-AMPS), and a further development of the north-american 1G mobile system AMPS. It was once prevalent throughout the Americas, particularly in the United States and Canada since the first commercial network was deployed in 1993. D-AMPS is considered end-of-life, and existing networks have mostly been replaced by GSM/GPRS or CDMA2000 technologies.This system is most often referred to as TDMA.