Indian mobile phone firms signed 8.17 million subscribers in December, taking the wireless subscriber base in the world's fastest-growing telecoms market to 233.63 million, data from the telecoms regulator showed.

That was slightly below the 8.32 million users added in November, the Telecom Regulatory Authority of India said in its monthly report released on Tuesday evening.

Wireless subscriber numbers surged 56 percent in 2007 from 149.62 million at the end of 2006, the report showed.

India's mobile firms have been signing about 8 million users each month since July, lured by call rates as low as 1 U.S. cent a minute and by cheap handsets.

Still, only about a quarter of the population has a phone, and the government has a target of 500 million phones by 2010.

Sector leader Bharti Airtel Ltd added 2.20 million new users in December, taking its subscribers to 55.16 million.

Second-ranked Reliance Communications Ltd added 1.57 million users, lifting its subscriber numbers to 40.96 million, and Vodafone-controlled Vodafone Essar Ltd signed up 1.30 million users to take its customer base to 39.86 million.

Fixed-line telephone users declined to 39.25 million in the month from 39.31 million in November, extending a trend as subscribers turn to cheaper mobile phones.