Go to Urbandictionary.com and type "iPhone Killer". This is the definition you will get:
"Little is known of the iPhone Killer. Having never been seen in person, it is impossible to describe its appearance, nor has it even been proven to truly exist. There are many versions of the Legend of the iPhone Killer, each of which is wildly varied from the last. However, each and every version agrees that it is coming in a few months."
As it turns out, this is largely correct. The fabled iPhone killer is not unlike a mythical creature -- fascinating to think and talk about, but with no real proof of its existence.
If, over the years you have acquired a couple or more non-Apple smartphones, there is a good chance that at least one of them was labelled 'the iPhone killer' at some point. It is a marketing tagline, used by several device manufacturers over the years. The first iteration of the iPhone was launched 9 years ago, but no other smartphone since has been able to 'kill' it.
Apple unveiled the first generation iPhone in January 2007. Back then, normally there would be a gap of 2 to 3 months after a phone's launch before a rival would would announce plans to launch a competing product. During that period, users and reviewers would have had the time to use and give their verdict on a phone. But such was the hype around Apple's iPhone that within a mere two weeks of its launch, rivals Samsung and LG were announcing plans to make their "killer" versions of the phone.
The iPhone has always been owner's pride and neighbour's envy. Sure, iPhone has hardly ever been the phone with the best specification, but Apple's value as a brand which delivers premium product and experience has never been doubted. The criticism aimed at the iPhone has always been about specific modules such as lack of Bluetooth, the number of apps, RAM size, and megapixels in the camera.
The early iterations of the iPhone ran on OS X. Other manufacturers were also going through a lot of changes and the 'iPhone killers' of that era kept switching to different operating systems. There was Nokia launching 5800 and E71 on Symbian. Samsung was launching Omnia phones on Windows phone mobile and Instinct one. Even Blackberry was in the race for becoming the Apple assassin with its Blackberry Storm. Google, in the meantime, released their first Android phone, G1.
Sure, it is fair to compare your product to one of the best smartphones of the generation. Your phone might have some superior features compared to the iPhone and that's a great thing. But that doesn't really add up to making the whole package (your smartphone) as good or better than the iPhone.
One reason the iPhone is so popular is that it has been in a tightly bound system, with the operating system on the phone. Most of the features work seamlessly. Across generations and newer iterations, some things have stayed constant. And the major changes have been done over the iterations so that users never feel at sea. There has always been the assurance of picking up an iPhone and figuring things out in minutes. (Advanced options and settings can always be learnt over time.)
Early in 2010, Google launched the first Nexus. Initially, it too was dubbed the 'iPhone killer' but with time the Nexus line gained its own reputation. Google worked with many manufacturers on the Nexus series and still they managed to create an impression of a series with stock software and fast updates. Nexus 4 and Nexus 5 were huge hits for the company even with their few flaws. Just as iPhone is identified with Apple, Nexus began to get associated with Google. At some level, Samsung's Galaxy S series has also acquired that reputation but they still have a long way to go.
A lot of companies such as OnePlus with OnePlus One and 2, Xiaomi with Mi-series have claimed the iPhone Killer crown in recent times. Other companies such as Asus and Huawei have tried too. But if at all there have been real iPhone killers lurking around all these years, they have failed to 'assassinate' it. Apple is running stronger than ever.