Following a massive retail and advertising push, Samsung’s flagship Galaxy S III handset overtook Apple’s iPhone 4S as the world’s best-selling smartphone in the third quarter of this year, according to a Strategy Analytics survey. The Samsung phone sold an estimated 1.8 million units more than the iPhone 4S. Samsung’s lead will be short-lived as Strategy Analytics estimates that the iPhone 5 will become the world’s #1 smartphone in Q4.

Analysts previously estimated that the S III outsold the iPhone 4S, but only in the United States. Samsung stopped reporting device sales last year for competitive reasons and we also don’t know how many of the 18 million S III channel shipments ended up in customers hands. Still, that’s a nice accomplishment for Samsung, which earlier in the week confirmed beating its self-imposed goal of shipping 30 million S III units before year’s end…

Apple in the third quarter shipped six million units of the iPhone 5, the research firm estimates, in addition to 16.2 million iPhone 4S units. Though the two handset models outsold Samsung’s device, individually the S III was the best-selling smartphone model in Q3.

With 18 million S III units and an impressive 11 percent share of all smartphones shipped globally, Samsung’s phone has become the world’s best-selling smartphone model for the first time ever.

Note that S III total doesn’t include the recently unveiled four-inch S III Mini, S2, S or any other related models. The iPhone 4S total does not include the iPhone 5, iPhone 4 or any prior iPhone.

The research firm in a blog post wrote had to say this about the iPhone 5:

We expect the new iPhone 5 to out-ship Samsung’s Galaxy S3 in the coming fourth quarter of 2012 and Apple should soon reclaim the title of the world’s most popular smartphone model.

Here are the results, shipments-wise.

This is what the worldwide smartphone share looked like in Q3 2012.

There are a couple of reasons for such an outcome.

Firstly, a lot of people held off purchasing the one-year old iPhone 4S in light of the expected iPhone 5 upgrade.

Secondly, Samsung’s phone has been five months on the market now and is widely available across carriers and world markets. The fact that it has a massive screen, a speedy chip and supports 4G LTE didn’t hurt either.

Thirdly, Samsung is a big spender when it comes to advertising. S III ads can be seen everywhere, from television to underground stations to huge billboards in frequent locations to sponsorships of massive sports events. In short, there is no escaping the all-pervasiveness of Samsung’s advertising. Samsung likely benefitted from its anti-Apple commercials as well.

And finally, it is no secret that telcos love the S III and are positioning it as the best iPhone alternative amongst the crop of Android handsets that mostly look the same, with little differentiation in terms of feature. Samsung has done a nice job of developing its own software features that mimic Siri while offering headline capabilities such as interesting sharing options, motion control and more.

I got my S III recently and am pleasantly surprised with the overall package, but I like my iPhone better.

You?