The Android operating system grew by nearly 900% in 2010

"In the smartphone operating system (OS) market, ''Android grew 888.8 percent in 2010 and moved to the No. 2 position. Android sales in the fourth quarter of 2010 continued to be driven by broad availability of many high-end products from HTC (Desire range, Incredible and EVO), Samsung (Galaxy S) and Motorola (Droid X, Droid 2).
Symbian’s market share dropped further in the fourth quarter of 2010 to 32.6 percent or 32.6 million units. This allowed Android to overtake Nokia's Symbian unit sales during the fourth quarter of 2010. However, the Symbian OS is also used by Fujitsu and Sharp as well as in legacy products from Sony Ericsson and Samsung. “This aggregated volume kept Symbian slightly ahead of Android,” said Ms. Cozza.
The wider availability of the iPhone 4 helped Apple to maintain its share of the smartphone market to 16.0 percent in the fourth quarter 2010 and led the iPhone OS platform to reach the No. 4 position in 2010. "As a platform, iOS is in excellent shape," said Ms. Milanesi. With every iPad and iPod Touch sold, Apple increases the profile of iOS with potential iPhone buyers and strengthens its developer ecosystem."
Source:  Press release from Gartner, 9th February 2011