What is 2G Spectrum?
2G is ‘Second Generation’ wireless telephone technology.
After the launch of 2G, we tend to call the earlier basic service as 1G.
2G obviously more efficient on the spectrum allowing for far greater penetration. In 1G network signals are analog while it is digital in 2G.
It increases system capacity as digital voice data can be compressed and multiplexed more effectively, thus allowing more calls to be backed into the same amount of radio bandwidth.
Most importantly the digital system emit less radio power from the handsets.
Also, we all know digital means increased sound quality.
Beyond 2G there is 3G (Third Generation) Higher data speeds and 4G in developed countries.
The first Pre-Commercial 3G or Third generation was launched in Japan by NTT DoCoMo in Japan in May 2001.
In India MTNL started 3G enabled mobile service in 2008.
There is going to be auction for 3G in India soon.
With Government FDI norms relaxed, Google is intending to bid with an Indian partner.
for detailed reading visit http://www.three-g.net/
you may also refer wikipedia