What is the 2G spectrum scam about?

What is the 2G spectrum scam about?: "The issue dates to 2008 when nine telecom companies were issued scarce airwaves and licences for second generation (2G) mobile phone services at Rs.1,658 crore (less that $350 million) for a pan-India operation. As many as 122 circle-wise licences were issued.
The opposition said that by giving the airwaves cheap, that too in the controversial manner of first-cum-first-served basis, the exchequer had lost billions of dollars. The cut-off date for applications was also arbitrarily advanced.

Later, based on the auction of airwaves for third generation (3G) services, which got nearly $15 billion to the exchequer, and that for broadband access, which fetched over $8.5 billion, the notional loss was estimated at $38 billion to the exchequer.
But Prime Minister Manmohan Singh himself defended Raja’s decision and said May 24 that all that his communications minister had done was to implement a policy already in place and none of the norms were flouted."