The main difference between 1G and 2G is that the radio signals used by 1G networks are analogue, while 2G networks are digital. Although both use digital signalling to connect radio towers (which listen to handsets) to the rest of the telephone system, voice itself during a call is encoded to digital signals in 2G, whereas in 1G it is only modulated to higher frequency, typically 150MHz and up. The inherent advantages of digital technology over that of analogue meant that 2G networks eventually replaced these almost everywhere.
Second-generation, or 2G, mobile telecom networks were commercially launched in 1991. Three primary benefits of 2G networks over their predecessors were that, phone conversations were digitally-encrypted, 2G systems were significantly more efficient on the spectrum, allowing far greater mobile phone penetration levels, and 2G introduced data services for mobile, starting with SMS text messages.
2G technologies enabled various mobile phone networks to provide services such as text, picture and multimedia messages (MMSes). All text messages sent over 2G are digitally encrypted, allowing for transfer of data in such a way that only the intended receiver can receive and read it.
2G has been superseded by newer technologies such as 2.5G, 2.75G, 3G and 4G; however, 2G networks are still used in many parts of the world.
3G, short for third generation, is the third generation of mobile telecommunications technology. The first 3G networks were introduced in 1998. This technology is based on a set of standards used for mobile devices, and mobile telecommunications use services and networks that comply with International Mobile Telecommunications-2000 (IMT-2000) standard specifications by International Telecommunication Union. 3G finds application in wireless voice telephony, mobile Internet access, fixed wireless Internet access, video calls and mobile TV.