Image source: Getty Images

This month marks the 10-year anniversary of the iPhone. Although smartphones existed before Apple's (NASDAQ:AAPL) invention, the iPhone brought us into a whole new era of smartphones, practically redefining the category and pushing dominant feature-phone makers such as Nokia (NYSE:NOK) into near irrelevance. These devices, combining a pocket computer and an internet communicator, proved immensely popular, accelerating mobile-phone adoption, particularly in emerging markets. 

Apple has largely dominated the smartphone market over the past 10 years, but one competitor has made significant progress over the past five years or so: Samsung (NASDAQOTH: SSNLF), which has become a fierce competitor to Apple with its flagship Galaxy line of smartphones. Several other competitors have had modest success as well, but Apple dominates the list of the five best-selling smartphones of all time, which we've compiled here with the help of some data from The Telegraph.

 

Image source: Apple.

5. iPhone 4s

The iPhone 4s marked Siri's introduction. Aside from the Apple voice assistant, the iPhone 4s didn't represent a major step up from the iPhone 4. It featured the same design with a beefed-up processor and better camera.

But it was the first iPhone to be released across all four major wireless carriers in the United States and sported a wide global release as well. On top of that, the iPhone 4s was the first iPhone model Apple released in October, coming 16 months after the release of the iPhone 4. That may have led to greater pent-up demand for the device.

Image source: Apple.

4. iPhone 5

The successor to the iPhone 4s boasted a larger 4-inch display (compared with 3.5 inches in its predecessors), while increasing the height of the phone by only about 0.3 inches. The form factor proved so popular that Apple continues to use it in the iPhone SE four years later.

What makes the iPhone 5's sales success more impressive is that it was discontinued after just one year, replaced by the iPhone 5c. Still, it managed to sell over 70 million units in those 12 months, and its successors continue to sell today.

Image source: Samsung.

3. Samsung Galaxy S4

The Galaxy S4 capitalized on the popularity of the Galaxy S3, using the same design with upgraded internal hardware. The big new features of the Galaxy S4 were all software based, such as the ability to detect when a finger is hovering over the screen and advanced eye tracking.

Despite a lack of excitement from critics, the upgraded phone managed to hit 10 million unit sales in half the time of its predecessor -- just 27 days. It went on to sell over 80 million units.

Image source: Nokia.

2. Nokia 5230

Nokia released an entry-level smartphone in 2009 dubbed the 5230. (Nokia has always been very creative with its phone names.) The phone lacked Wi-Fi capabilities, sported a small 3.2-inch touchscreen and a low-resolution camera, and ran Nokia's Symbian OS. But the lack of features allowed Nokia to keep the price extremely low, which helped it sell a lot of units in emerging markets.

Overall, Nokia managed to sell over 150 million 5230s before discontinuing it.

Image source: Apple.

1. Apple iPhone 6 and iPhone 6 Plus

The iPhone 6 represented a major step up from the iPhone 5s. It came in two sizes -- 4.7 and 5.5 inches -- which satisfied a significant pent-up demand for a large-screen iPhone. It was also the first iPhone with a near-field-communications chip, enabling Apple to introduce Apple Pay.

The iPhone 6, with its larger screen, proved extremely popular in Greater China, leading to an 84% increase in Apple's sales in the region. It was just as popular everywhere else, too, getting many older iPhone users to upgrade their devices. Overall, Apple sold more than 220 million iPhone 6 units.

Image source: Apple.

What's next?

Apple is expected to release a special 10th-anniversary edition of the iPhone this fall, and many analysts are expecting another "super cycle" on the level of the iPhone 6. With a significantly larger installed base compared with 2014 -- ahead of the iPhone 6 release -- there may be a lot more consumers looking to upgrade their phone if Apple releases a compelling new phone.

Meanwhile, Samsung has split its sales between the Galaxy S and Galaxy Note lines as the competition for high-end Android phones continues to improve. It'll be hard for Samsung to make another phone that's able to get on the all-time best-seller list, especially in light of the recent trend of poor sales following its exploding Galaxy Note 7 fiasco.

Indeed, Apple is the front-runner to make the next top-selling smartphone, though it still faces stiff competition from the collective Android phone manufacturers.

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This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.

Adam Levy owns shares of Apple. The Motley Fool owns shares of and recommends Apple. The Motley Fool has a disclosure policy.