what is a 3-G or 4-G phone exactly . what is the concept and its advantages

Evolutionary line of cell phone technology standards has spanned from 1G, 2G, 2.5G to 3G, 4G describes the entirely new world beyond advanced 3G networks. 4G - also known as “beyond 3G” or “fourth-generation” cell phone technology, is new evolution and complete 3G replacement in wireless communications. Just as data-transmission speeds increased from 2G to 3G, the big jump from 3G to 4G promises even higher data rates than existing previous generations. 4G promises voice, data & high-quality multimedia in real-time (“streamed”) at any time and anywhere. Telecom regulatory bodies estimate launching of 4G networks commercially between 2012 and 2015.