The 2G networks mostly cover GSM and GPRS based networks. The Global System for Mobile communications or GSM uses digital modulation to improve voice quality but the network offers limited data service.
2G carriers have improved transmission quality and coverage than their predecessors. The 2G carriers also offer additional services, such as paging, faxes, text messages and voicemail. The limited data services under 2G included WAP, HSCSD and MLS.
An intermediary phase, 2.5G was introduced in the late 1990s. It uses the GPRS standard, which delivers packet-switched data capabilities to existing GSM networks. It allows users to send graphics-rich data as packets. The importance for packet-switching increased with the rise of the Internet and the Internet Protocol. The EDGE network is an example of 2.5G mobile technology.
The 3G network allow mobile telephone customers to use audio, graphics and video applications. Over 3G it is possible to watch streaming video and engage in video telephony, although sometimes such activities are constrained by network bottlenecks and over-usage.
The 3G phones deliver up to 2 Mbps, but only under the best conditions and in stationary mode. Moving at a high speed can drop 3G bandwidth to 145 Kbps.
3G cellular services, also known as UMTS, sustain higher data rates and open the way to Internet based applications. 3G technology supports both packet and circuit switched data transmission, and a single set of standards can be used worldwide with compatibility over a variety of mobile devices. UMTS delivers the first possibility of global roaming, with possibility of access to the Internet from any location.