This is a little history of the cell phones that people enjoy using today.

In the 1990s, 'second generation' (2G) mobile phone systems such as GSM, IS-136 ("TDMA"), iDEN and IS-95 ("CDMA") began to be introduced. 2G phone systems were characterized by digital circuit switched transmission and the introduction of advanced and fast phone-to-network signaling. In general the frequencies used by 2G systems in Europe were higher than those in America, though with some overlap. For example, the 900 MHz frequency range was used for both 1G and 2G systems in Europe, so the 1G systems were closed down to make space for the 2G systems. In America the IS-54 standard was deployed in the same band as AMPS and displaced some of the existing analog channels.