There's no stopping the Apple Inc. express. Apple, the world's top tech company by market value, passed by nemesis and supplier Samsung Electronics to become the world's biggest smartphone vendor in the fourth quarter of 2011.

Surging demand for the iPhone 4S and rival smartphones is helping offset the impact of the global economic crisis on consumer spending. Market research firm Gartner Inc. says worldwide smartphone sales to end users soared to 149 million units in the fourth quarter of 2011, a 47.3 per cent increase from the fourth quarter of 2010. Total smartphone sales in 2011 reached 472 million units and accounted for 31 percent of all mobile devices sales, up 58 percent from 2010.

According to Gartner, smartphone volumes during the quarter rose due to record sales of Apple iPhones. As a result, Apple became the third-largest mobile phone (smartphones plus basic phones) vendor in the world, following Nokia and Samsung. Apple also became the world's top smartphone vendor, with a market share of 23.8 percent in the fourth quarter of 2011, and the top smartphone vendor for 2011 as a whole, with a 19 percent market share.

Gartner, however, expects Apple's market share to slip for a couple of quarters as novelty of the iPhone 4S wears out.

The research firm said, "Apple had an exceptional fourth quarter, selling 35.5 million smartphones to end users, a 121.4 percent increase year on year. Apple's continued attention to channel management helped it take full advantage of the strong quarter to further close the gap with Samsung, which saw some inventory build up for its smartphone range. Apple's strong performance will continue into the first quarter of 2012 as availability of the iPhone 4S widens. However, since Apple will not benefit from delayed purchases as it did in the fourth quarter of 2011, Gartner analysts expect its sales to decline quarter-on-quarter."

In October, just weeks following the death of Apple's iconic founder, Steve Jobs, the Cupertino, California released the iPhone 5. Selling a record four million units in the first three days, the iPhone 4S sports a 3.5-inch screen; an 8-megapixel, 1080p high-definition camera; an A5 dual-core chip processor that has a graphics processor that's seven times faster than its predecessor.

While the revolutionary digital assistant Siri and the more advance camera have impressed many Apple fans -- and thus enticed many iPhone users to upgrade, and Android and BlackBerry users to convert to the latest iPhone, the iPhone 4S may not find the same long-term success as its predecessors for a number of reasons: the iPhone 4S looks exactly alike the iPhone 4; its 3.5-inch screen is dwarfed by the 4-inch-plus screens of Android phones like the Motorola Droid 4 and the Galaxy S 2; the iPhone 4S lacks a 4G-LTE connection, and its battery don't last as long as advertised.

Eroding sales of the iPhone 4S could force Apple to returning to its previous schedule of releasing the iPhone 5 in June (or earlier), instead of waiting until October, exactly a year after the iPhone 4S was released.

Sure Apple will likely continue to beat Wall Street estimates even if it doesn't do an iPhone refresh earlier than expected, as the iPad and the Macs continue to post double digit growth. But the iPhone's impact on sales has been soaring each quarter. iPhone sales accounted for 53% of the 46.3 billion of revenue in the quarter ended Dec. 31, 2011, compared with just 39% of revenue in the same period in 2010.

An iPhone with a bigger, 4-inch-plus, screen is in the pipeline. Reports confirmed in October that the iPhone 5 was the last project that Steve Jobs was intimately involved with from concept to final design. But Jobs scrapped the project just months before the scheduled release on concerns that the bigger screen would fractured the iPhone market.

Apple chief Tim Cook hinted at the Goldman Sachs technology conference this week that Apple could be preparing to launch into the smart TV market with a revamped version of the Apple TV set-top box.

Sources from Apple's foreign supply chains in China and Taiwan said last month they have already begun production on the company's next iPad, presumably called "iPad 3," and a Foxconn employee said his factory is "gearing up" to begin production on the next iPhone.

And yes, there's no stopping the Apple express.