A Weird Headphone Jack Situation
The iPhone was one of the first phones to feature a standard-sized 3.5mm jack that could theoretically be used with any headphones, but since it also supported a microphone for hands-free calls, it seems that Apple wanted to make sure users didn’t run into compatibility problems.
As a result, it recessed the headphone jack on the first iPhone in such a way that only Apple’s own included earbuds could be plugged in. Most other headphones didn’t have a thin enough end, and as a result there quickly became a wealth of third-party adapters that existed for no other purpose than to extend the standard 3.5mm headphone connection to make it fit into the iPhone’s narrow jack.
Fortunately, Apple must have realized that this was pretty silly — there was no reason that standard stereo earphones should have presented a problem with the headphone jack, since the microphone was the third wire — and by the following year the iPhone 3G had gained a more normal flush headphone jack, which would be the normal until Apple decided to remove it entirely with the iPhone 7, returning us back to the era of headphone adapters.