Worldwide sales of smartphones to end-users totalled 329.67 million units, an increase of 13.5 percent from 290.38 million units in the same period in 2014, Gartner said in a statement.
"While demand for lower-cost 3G and 4G smartphones continued to drive growth in emerging markets, overall smartphone sales remained mixed region by region in the second quarter of 2015," Gartner Research Director Anshul Gupta said.
Emerging Asia/Pacific (excluding China), Eastern Europe and Middle East and Africa were the fastest-growing regions, driven by good performance from Chinese and local vendors, he added.
By contrast, smartphone sales in China fell for the first time year over year, recording a four percent decline.
"China is the biggest country for smartphone sales, representing 30 percent of total sales of smartphones in the second quarter of 2015. Its poor performance negatively affected the performance of the mobile phone market in the second quarter," Gupta said.
He added that China has reached "saturation", its phone market is essentially driven by replacement, with fewer first-time buyers.
"Beyond the lower-end phone segment, the appeal of premium smartphones will be key for vendors to attract upgrades and to maintain or grow their market share in China," he said.
Samsung led the tally with 21.9 percent share in the April-June 2015 quarter, followed by Apple (14.6 percent), Huawei (7.8 percent), Lenovo (five percent) and Xiaomi (4.9 percent).
The total mobile handset market (feature and smartphones) grew marginally to 445.75 million units in the said quarter from 444.19 million units in the April-June 2014 quarter.
Samsung led the total market with 19.9 percent, followed by Apple (10.8 percent), Microsoft (6.2 percent), Huawei (5.9 percent), LG Electronics (4 percent), Lenovo (3.7 percent), Xiaomi (3.6 percent), TCL Communication (3.5 percent), ZTE (3.3 percent) and Micromax (2.2 percent).