We’ve seen handset makers like HTC, LG and Nokia all warning of declines in smartphone sales. But if there is a slowdown affecting some, it’s not because people are not buying smartphones; it’s because they’re all buying iPhones.

Figures out from Gartner today say that smartphone sales totalled 149 million units in Q4 2011 — 47.3 percent higher than the same quarter a year ago, led by none other than Apple’s iPhone, which its analysts noted “saved” the smartphone market after two quarters of declining sales.

The mobile device market is also getting ever closer to a tipping point in terms of smartphone dominance: Gartner notes that they accounted for one-third of all mobile sales in the last quarter worldwide. The analysts predict that in 2012 smartphone sales will continue their march, growing by 39 percent compared to only seven percent growth for feature phones.

That is significant in that it shows how strong smartphones are playing in developing markets as well. In developed markets like the U.S., UK and Japan smartphone sales have been close to or already outpacing feature phone sales for a little while now.

Platforms. Moving away from specific vendors, Google’s Android platform grew even more dominant, and accounted for more than 50 percent of all smartphones sold, up from 30 percent a year ago. Apple’s iOS and bada from Samsung were the only other two platforms that grew in market share, with the rest all continuing to see big declines, including the Windows Phone platform from Microsoft, which accounted for 1.9 percent of sales.

Apple. On the strength of tremendous iPhone sales in the U.S. and Europe, Apple became the world’s biggest smartphone vendor, with a 23.8 percent share of all sales in Q4, which works out to unit sales of 35.5 million smartphones.

Apple is now also the third-largest mobile phone vendor in the world overall. That’s notable especially considering that the two vendors ahead of Apple, Samsung and Nokia, are also selling a range of much less expensive devices.

But one word of caution to note here, too: Gartner doesn’t expect Apple to have a blockbuster quarter like this again soon — saying that a lot of the boost was due to pent-up demand from consumers awaiting the newest model of the iPhone, which turned out to be the iPhone 4S. Famous last words or the canary in the coalmine?

Losers. More bad news for LG, Sony Ericsson, RIM and the newest charm on Google’s bracelet, Motorola: all saw declines in market share — not only because of fierce competition from Apple and Samsung in mature markets but also because of price pressure in developing markets from the likes of ZTE and Huawei.

The sub-$100 smartphone is only going to become a more prevalent theme in the future, and companies like RIM will have to address that if they hope to claw back some of their old leadership. (Yes, there is an irony here: Apple doesn’t dabble in cheap devices — putting aside handset subsidies that carries put on a range of devices, including the iPhone.)

What of Nokia? Still on top in the overall rankings by a good margin, and not losing nearly as much steam as you would have expected, given all the doom and gloom that gets reported. Its share is now at 23.4 percent compared to 27.1 a year ago. Indeed, in its last quarterly earnings, Nokia actually showed quite good results for sales of its feature devices, even as it saw huge smartphone declines. Samsung inched up a couple of percentage points to 19.4 percent of all sales — a testament to its strong Android-based smartphone sales and its equally strong line of feature phones built using its proprietary bada OS.