The wireless network that is referred to in terms of connectivity of mobile telephones is an alternative to connections that rely on copper wire and often uses radio transmission. 3G stands for Third Generation Wireless, indicating that two other generations of standards have preceded it: 1G, an analog system developed in the 1960s and 1970s, and 2G, a digital system that began being developed towards the end of the 1980s. 3G systems are those that are made to meet the International Telecommunication Union (ITU) standards for mobile telephone systems of the third generation, under the IMT (International Mobile Telecommunications program IMT-2000.
Experts disagree both about whether IMT-2000 led to a set of 3G systems that combine coherence with flexibility or the grouping of incompatible items that has left the systems competing for dominance. In any case, there are a number of different 3G systems although the number differs depending on who one reads. Across accounts, they include CDMA 2000 (Code Division Multiple Access), HSDPA (High Speed Downlink Packet Access), TD-SCDMA (Time Division-Synchronous Code Division Multiple Access), UMTS (Universal Mobile Telecommunications Systems), and W-CDMA (Wideband Code Division Multiple Access).
CDMA can transmit multiple signals over the same frequency simultaneously and is the underlying technology in three 3G systems: CDMA 2000, HSDPA, and WCDMA, the latter two of which are used by GSM (Global System for Mobile communication) carriers. In 2009, there were 460 million customers with CDMA itself, with half of these being in Asia. In the United States, Verizon® and Sprint® both use CDMA, while AT&T® and T-Mobile® use HSDPA. UMTS is a GSM standard that uses WCDMA and HSPA.
3G systems all are able to provide data rates that vary with the situation. The expectations in the standards are 144 kbps (kilobytes per second) or more in quick moving vehicular traffic, 384 kbps for pedestrian traffic, and 2 MBps (megabytes per second) for indoor — that is, nearly stationary — phone use. They all are enabled to determine the location of mobile phones. And they all support multimedia in a variety of ways.
The Fourth Generation Communications System is under development and is expected to be fully implemented between 2012 or 2013 and 2015, by various estimates. As of 2010, two competing technologies were being deployed. One is LTE (Long Term Evolution). Another is WiMAX (Worldwide Interoperability for Microwave Access). Both of these 4G networks were already beginning to replace 3G in locations around the world in 2009–2010.