Greater China also became Apple's largest volume market, ahead of North America, thanks to strong sales in China during the first quarter of 2015.

Gartner noted that the fastest growing regions were emerging Asia/Pacific, Eastern Europe, and the Middle East and North Africa. Due to these high-performing regions, the emerging markets achieved a 40 percent increase in sales during the first quarter of 2015.

"During this quarter, local brands and Chinese vendors came out as the key winners in emerging markets," said Anshul Gupta, research director at Gartner. "These vendors recorded an average growth of 73 percent in smartphone sales and saw their combined share go up from 38 percent to 47 percent during the first quarter of 2015."

"Apple’s extension into more Asian markets helped it close the gap with Samsung globally. In the same period last year, there was a difference of more than 40 million units with Samsung; this difference has been halved, within one year, to just over 20 million units," said Mr. Gupta.

Amongst the top five global smartphone vendors, Samsung continued to see a decline in sales and share during the first quarter of 2015. "Despite a weak first quarter globally, Samsung's performance returned to growth quarter-on-quarter, with an 11 percent increase from the fourth quarter of 2014. We expect Samsung's drop rate to be slower than that seen in recent quarters with sales of its new S6 smartphones starting in the second quarter of 2015, and its Galaxy Alpha receiving good response," said Mr. Gupta.

In the smartphone operating system (OS) market, Android's share fell by 1.9 percentage points, while iOS grew year-on-year for the third consecutive quarter. "Strong iPhone sales in China during the first quarter of 2015 had an impact on Android's performance in that country. Android’s volumes fell by 4 percent year-on-year in China for the first time," said Roberta Cozza, research director at Gartner.

“The performance of Windows Phone remained flat, mainly due to a weak ecosystem and a less desirable mobile brand, together with a strong and established competitive smartphone market. The upcoming Windows 10 will create a consistent user experience across all devices, but it remains to be seen whether developers will follow.”

With the features and core capabilities of OSs evolving rapidly and becoming increasingly similar, it is now critical for OS providers to find ways to differentiate themselves. They need to extend their OS ecosystem's reach by adding new functionalities, and build platforms that can span multiple devices types.

Worldwide mobile phone sales to end users totaled 460.3 million units during the first quarter of 2015, a 2.5 percent increase from the same period in 2014. "In light of their strong smartphone sales in the emerging markets, the Indian and Chinese phone manufacturers increased their footprint during the first quarter of 2015. Six of them were in the top 10 in the first quarter of 2015," said Mr. Gupta.