1G
In mobile telephony, first-generation systems were analog, circuit-switched. Voice links were poor, handoff unreliable, capacity low, and security non-existent. 1G systems are not now under active development – indeed, in some areas 1G spectrum is being auctioned for 2G and 3G use.

2G
In mobile telephony, second-generation protocols use digital encoding and include GSM, D-AMPS (TDMA) and CDMA. 2G networks are in current use around the world. These protocols support high bit rate voice and limited data communications. They offer auxiliary services such as data, fax and SMS. Most 2G protocols offer different levels of encryption.
2.5G
In mobile telephony, 2.5G protocols extend 2G systems to provide additional features such as packet-switched connection (GPRS) and enhanced data rates (HSCSD, EDGE).
3G
In mobile telephony, third-generation protocols support much higher data rates, measured in Mbps, intended for applications other than voice. 3G networks trials started in Japan in 2001. 3G networks are expected to be starting in Europe and part of Asia/Pacific by 2002, and in the US later. 3G will support bandwidth-hungry applications such as full-motion video, video-conferencing and full Internet access.