Vodafone India, the country's second-largest telecom operator, will expand its 4G services to metros Mumbai, Delhi, Bengaluru and Kolkata by March next year.

While Bharti Airtel has already increased its 4G network to over 300 towns across the country, Vodafone 4G's presence is currently limited to only 10 towns in Kerala.

"Vodafone will increase the intensity of its 4G rollout covering important metros — Mumbai, Delhi, Bengaluru and Kolkata — before March 2016," the company said in a statement.

In August, the company had said it would roll out 4G services in the four metros as well as Kochi by the end of December.

"Testing of 4G services in these locations has already commenced successfully and Vodafone India has partnered with leading global technology service providers for the network roll-out," IANS quoted the statement as saying.

Bharti Airtel and Vodafone India are the leading players in the top five data markets — Mumbai, Delhi, Kerala, Karnataka and Tamil Nadu — where the APRU is Rs 225, up 40% compared to the industry average of Rs 161.

But the launch of 4G services of Reliance Jio are expected to pose significant risks to market shares of the top two telecom operators, Bharti Airtel and Vodafone India, as their high-value subscribers may become "early adopters" of the high-speed data services offered by the telecom arm of Mukesh Ambani's Reliance Industries, according to global brokerage firm CLSA.

Of the two, Vodafone is more vulnerable to Reliance Jio's services as it holds limited 4G spectrum, CLSA said.

As revenue from voice services becomes flat, telecom operators will vie to gain premium data customers in the coming months.

Going forward, the long-term growth of telcos is likely to be led by mobile data usage, the revenue from which is projected to increase three times to $14 billion (Rs 93,800 crore) in FY18 from FY15, it added.

Analysts say increased competition in the data services will likely lead to further increase in capital expenditure by the operators to keep growth intact. Telecom companies are also expected to purchase spectrum from others at a higher price, resulting in increased debt levels.