Google's Android mobile platform topped Microsoft in the last quarter and it is closing in on Apple in smartphone sales. Apple's iPhone, however, is still ahead of Android globally, by more than three million units, according to research firm Gartner.

Android was the fourth most popular operating system on smartphones sold in the first quarter, Gartner is reporting, putting Google in a strategic position as handsets appear ready to surpass computers for browsing the Web. In North America, Android's sales grew 707% compared to the same period last year, from 575,000 to 5.2 million units.

Apple, ranking third, had its strongest quarter yet as sales increased by 112.2% , with 8.3 million units sold in the first quarter, which was more than twice as many units sold during the same timeframe last year. The iPhone's popularity is greater than Android-based devices in Europe and Asia, according to Gartner.

Nokia's Symbian remained in the top position worldwide with 24.1 million units sold due in part to its low-priced smartphones, but the platform is not growing as fast as the competition. Research in Motion followed, with sales of 10.6 million units.

Gartner is predicting the Android will surpass Apple soon as there are more handset makers using its operating system, and Android phones are already outselling the iPhone in North America. More startups are developing applications for the Android, further boosting interest among consumers.

Research group NPD said earlier this month that smartphones running on Android accounted for 28% of U.S. unit sales in the first quarter, ahead of the iPhone, but Apple questioned the figure and said it was based on a limited sample of consumers. Total worldwide mobile phone sales were 314.7 million units in the first quarter of 2010, an increase of 17% over last year.

Handset manufacturers such as Samsung, HTC, and Motorola all make Windows phones but are increasingly turning to Android, which is not only free, but attracting a fast-growing developer community. Microsoft is the only major phone software maker that charges handset makers a license fee.