Apple is rumored to ditch the 3.5mm headphone jack from the next iPhone. This would allow the phone to be more than a millimeter thinner.
This year Apple decided to add the 3D Touch to the iPhones and shrink the battery size. According to the rumors, the iPhone 7 would not have a 3.5mm headphone jack to be even thinner. That would also mean smaller battery.
The current iPod Touch is 1mm thinner than the iPhone 6S and it still has a headphone jack. According to the rumors, iPhone 7 would be more than a millimeter thinner than the current iPhone 6S.
To replace the headphone jack, Apple would use the Lightning port and the iPhone 7 would ship with earbuds with a Lightning connector. For 3rd party headphone makers this would not be easy thing. The headphones use analog signal and the Lightning port is digital. The adapter could be quite large and ugly unless the headphones are specially made for the new iPhone and would be incompatible with other devices. Attaching some current headphones to the iPhone 7 would always need an adapter.
Apple is really pushing its limits. We know that many people think that everything Apple does is right but in this case some might make the switch to another smartphone because of the ridiculous quest of thinness. Most of people want battery life, not thinness, especially if it brings things like Lightning headphones.
Source: Macotakara (Japanese)
Photo: iFixit teardown