India's telephone customer base has crossed the 500 million mark 15 months ahead of target, official figures released Wednesday showed.

The government had forecast India would hit half a billion phone users by the end of 2010, but it crossed this level in September, the Telecom Regulatory Authority of India (TRAI) figures showed.

"The set target of 500 million telephones by the end of 2010 has been achieved by September 2009," the regulator said in a statement on its website.

The number of telephone customers in India rose to 509.03 million at the end of September from 494.07 million in August. This takes total density to 43.50 percent in the country, whose population stands at nearly 1.20 billion.

Mobile density stands at 40.31 percent as mobile operators added 14.98 million users in September alone.

Growth in the telephone market -- mainly driven my mobiles -- has been blistering since 2000 and outpaced all forecasts.

Total telephone density stood at just 2.8 percent in 2000 and registered eight percent in 2004.

The country is the second-biggest market for cellular services after China, which has more than 600 million users. India is the fastest-growing mobile market in the world.

Mobile operators led by Bharti Airtel, Vodafone Essar and Tata Teleservices have been luring customers with cheap tariffs of less than one cent a minute.

Rock-bottom calling rates have been the main driver of India's cellular phone boom.

In a bid to draw new mobile customers, operators which only used to offer per minute rates are introducing per second billing, reducing call costs further.

But the fierce competition has been putting pressure on Indian telephone companies' earnings and analysts predict consolidation in the crowded market.