Smartphones continue to be the fastest-growing mobile device segment in the third quarter with sales surpassing 41 million units worldwide, representing a 13 percent jump over the same period last year. That compares to overall total phone sales of 308.9 million, which increased 0.1 percent over last year, Gartner reports.

As smartphone sales ramp, the competition is heating up between the various handset vendors. Nokia’s worldwide smartphone share reached an all-time low of 39 percent in Q3; BlackBerry-maker Research In Motion’s share reached 20 percent, a record high, and Apple’s iPhone share reached 17 percent, gaining slightly more than four percentage points. As for other platforms: Android’s share totaled 3.5 percent and Windows Mobile 6.5 didn’t come out in time to have impact Microsoft’s results, which fell again in the quarter.

Gartner said Nokia’s loss in market share negatively affected the Symbian operating system. Meanwhile, RIM’s sales volumes soared with the help of the Curve 8900 launching in Europe and the Tour and Storm 2 with Verizon Wireless (NYSE: VZ) in the U.S. RIM (NSDQ: RIMM) also focused on pre-paid sales in emerging markets like Latin America. Sales of the iPhone are expected to increase in Q4 as Apple (NSDQ: AAPL) starts selling the device in new markets, including China and in 16 other countries. It also added an additional carrier in the UK.