Mobile technology is based on dialogue between the cell and the handset with a digital stream of data that is made up of digitised audio, except for those first generation ones that used analogue networks. Basically, the technology that is able to achieve this really depends on which network the operator of the mobile phone has literally adopted.
This mobile technology is commonly grouped by generation. The initial technologies started way back in 1979 in Japan, and were all analogue and also included NMT and AMPS. Then followed the second generation ones that were systems that began in 1991, Finland. They are all digitalised and also include CDMA, GSM, and TDMA.
The way the mobile technology is programmed renders many handsets vulnerable. At any moment when a mobile phone gets into an area with no coverage such as inside a tunnel, the phone sends out some sort of a reconnect signal to re-establish to the nearest transmitter, as well as identifying itself plus signalling that it is ready, again, to transmit. With the right equipment it becomes so easy to intercept a reconnected signal as well as encoding the data it now contains.
The 3G third generation mobile technology up to now being deployed started in 2001 in Japan. These devices are all digitalised amidst offering high speed access of data as well as voice services. Some operators now use some sort of a pre-designated band of frequency that is determined more by the requirements of the network and as also local regulations.