What's the best-selling smartphone in the world? According to a new report released today, the top spot for the third quarter goes to Samsung's flagship smartphone, the Galaxy S III, or S3 as some call it for short.

The report from Boston-based Strategy Analytics used research from its Country Share Tracker service. It found the Galaxy S III overtook Apple's iPhone 4S to become the best-selling smartphone in the recently completed third quarter. This is the S3's first time in that spot, but it may not enjoy that limelight for long.

The Samsung device shipped 18 million units worldwide in Q3, capturing 10.7 percent market share for smartphones. Its popularity with consumers and carriers in North America, Asia and Europe, is attributed by the research firm to its large touchscreen, as well as an extensive distribution channel in dozens of countries, and substantial operator subsidies.

In comparison with the Galaxy S3's 18 million units in the third quarter, Apple shipped an estimated 16.2 million of the iPhone 4S.

Waiting for iPhone 5

But Strategy Analytics echoes a widely held assessment that buyers held off buying Apple's 4S in the third quarter because they were waiting for the upcoming release of the iPhone 5.

During Q3 alone, the new iPhone 5 sold an estimated six million units. The research firm said it expects the iPhone to regain its title as the most popular smartphone in fourth quarter. In the first three days of the iPhone 5's availability in stores, for instance, Apple sold about five million units.

Nevertheless, the popularity of the Samsung device is clearly growing by leaps and bounds. Its third quarter sales were more than triple the 5.4 million units sold in the second quarter. Its market share also tripled, increasing from 3.5 percent up to 10.7.

In the five months since its release, the Galaxy S3 has sold 30 million units, including worldwide pre-orders of over nine million, and Samsung, like Apple, has pursued a strategy of releasing it widely through multiple carriers. In fact, the S3 has clearly established itself as the iPhone's main competitor.

The Venerable Galaxy S Line

The competition, and the many comparisons in industry press between the two devices, is also being carried out in courtrooms, as the S3's interface and other features figure into the continuing worldwide legal battle between Apple and Samsung over intellectual property rights.

The first Galaxy S was released in 2010, and the company's Galaxy S II and Galaxy Tab have also sold well.

The S3 uses the Android 4.0 operating system, also known as Ice Cream Sandwich. It offers a large, 4.8-inch high-definition Super AMOLED screen with up to 720p resolution, and boasts 2 GB of memory Relevant Products/Services and 4G LTE.

Like the iPhone's Siri, the Galaxy S3 has an intelligent voice agent called S Voice that accepts verbal commands. For example, if the phone's alarm rings, a user can say "snooze" to the phone to turn it off. S Voice also accepts commands to play specific songs, turn up the sound volume, organize your schedule or send emails, among other functions.