In the second quarter of 2015, global smartphone sales in value terms was up 7 percent year-on-year, while in volume terms, it grew 5 percent year-on-year, GfK said in a statement.

"4G unit share was 58 percent globally in the second quarter of 2015, up from 26 percent in the second quarter of 2014. This represents a unit growth of 129 percent year-on-year, with China leading the global 4G ramp up," it added.

GfK forecasts that 4G smartphone penetration would continue to grow at the expense of 3G, which is currently at 38 percent of smartphone volume.

"India is expected to be the largest contributor of absolute smartphone unit growth globally this year," GfK Director (Trends and Forecasting) Kevin Walsh said.

GfK noted that there are significant regional differences in 4G take up: price polarization in North America, saturation in Western European markets, local brands tackling global players in India and China, and intense price competition in emerging markets.

In terms of geographies, North America saw volume sales grow 10 percent year-on-year, while Western Europe and China were up 9 percent and 49 percent year-on-year in the second quarter of 2015.

"India, in particular, has seen strong unit growth of 40 percent year-on-year, with local brands accounting for three of the top five smartphone vendor spots in the quarter," GfK said.

A number of Chinese smartphone brands have entered the Indian market this year, intensifying the already fierce competition between international and local vendors, it added.     

"The resulting price war is forcing average selling price (ASPs) down in a market where more than 80 percent of sales are in the low-end," it said.

In the second quarter of 2015, smartphone ASP in India declined 12 percent year-on-year.