According to the Department of Telecommunications of India, there were 346.9 million wireless telephones in India as of December 2008. Using a total population of 1,147,995,904 (July 2008 estimate), the penetration rate of cell phones was 30.2%. For comparison purposes, the penetration rate as of December 2007 was only 20.7%. In other words, the number of mobile phones in India increased by 113 million in 12 months, an astounding 48.5% growth rate.
You may also want to compare India’s mobile phone penetration to China’s mobile phone penetration.