The mobile market continued to grow in the second quarter of 2011 as worldwide mobile device sales rose 16.5% on year to total 428.7 million units, as smartphones accounted for a quarter of overall sales, a new report by technology research specialists Gartner suggests.

Smartphone sales grew 74% in the second quarter as consumers looked to entry-level and midrange Android handsets over feature phones, although sales actually declined quarter-on-quarter in Western Europe as the market showed “signs of fatigue”.

Google and Apple saw their operating systems increase in market share, with combined sales of Android and iOS devices nearly doubling to account for nearly 62% of smartphone sales in the quarter.

Nokia continued to dominate overall mobile sales but found its share decrease 7.5% year-on-year as Apple and upcoming Asian handset vendors began to eat into sales previously shared by the Finnish mobile giant, Samsung, LG and RIM. In the second quarter Apple, ZTE, HTC and Huawei were the only manufacturers to post increases in handset sales from the same period a year previous.

Apple’s sold nearly twice its number of units on year, rising from 2.4% to 4.6%, with ZTE overtaking Motorola and RIM to become the fifth biggest mobile vendor based on sales. Apple’s decision to expand its mobile carrier partnerships to 42 new operators and 15 new countries helped the Cupertino-based company’s growth, particularly in China where it is now the seventh largest mobile vendor and third-largest smartphone maker.

Smartphone sales increased to nearly 108 million units in the second quarter, with Google’s Android operating system increasing its market share 26.2 percentage points on year to hold 43.4% of smartphone sales in the second quarter. Nokia’s Symbian platform continued to decline – slipping from 40.9% to 22.1% – as the company looked to reduce excess stock and ready the company for its Windows Phone launches later in the year.

As a result of its destock of more than 9 million mobile phones overall and 5 million smartphones, Nokia held on to its position as the leading smartphone manufacturer by volume. In terms of sales, Samsung’s popular Galaxy S II handset helped the company become the third-largest smartphone manufacturer, with the handset contributing more than 5 million sales in the second quarter.

Aging products and a lack of new devices saw RIM’s share drop by 7 percentage points, as it conceded fifth position to ZTE. Despite the launch of new BlackBerry 7 and upcoming QNX handsets, competition from Apple’s new iPhone and new Android devices could see RIM face a difficult third quarter.

Gartner expects manufacturers to ease back on shipments in the second half of 2011, as the world’s financial markets enter an uncertain time. With this in mind, Gartner expects sales of mobile devices to grow around 12% in 2011.