In the US - one of Apple's largest markets - some 88% of iPhone owners who plan to change their mobile device during the next 12 months say they will stick with Apple, according to Kantar Worldpanel ComTech data. This article is copyright 2014 The Best Customer Guide.

However, in Apple's other largest market, China, 41% of iPhone owners who intend to change devices in the next 12 months say they will stick with Apple. For Samsung, 76% of owners in the US and 46% of owners in China say they will buy another Samsung device.

But with smartphone penetration approaching a ceiling in many mature markets, keeping customers loyal to the brand is only part of the challenge. Winning over the competitors' customers is what completes this equation.

In the US, smartphone penetration now stands at 55%, with smartphone sales representing 74% of overall mobile sales in Q1 2014.

When it comes to Apple and Samsung, most customer movement happens between the two, rather than toward other players. While 3.7% of current US Apple owners plan to move to Samsung, 8.5% of Samsung owners plan to move to Apple.

In China, the intended movement is significantly higher, confirming that the Chinese market is more volatile as subsidies do not help to regulate brand share. Some 35% of Apple's current owners in China are considering moving to Samsung, while 46% of Samsung's current smartphone owners are considering moving to Apple.

The latest big source of 'buzz' about the iPhone 6 is its larger screen size (the lack of which, many experts speculate, has caused Apple to lose appeal and customers over the past year). But Kantar Worldpanel ComTech data tells a different story when it comes to the US market: Among US consumers who upgraded their devices during the past year, only 14% of iPhone users moved from Apple to Android, and of those, only 2.1% opted for a screen of 5.5 inches or bigger. Among Chinese consumers, 39% left iOS for Android and, of those, 12.3% opted for a screen of 5.5 inches or larger.