As mentioned last week the rumours that Apple's next iteration of the iPhone will drop the headphone jack in favour of audio over the Lightning port are growing stronger.
There are good reasons for doing this, but I don't think they are the ones that Apple has in mind.
The headphone socket is as old as the hills, and despite its ubiquity doesn't do much other than allow the transfer of analog audio in and out of a device. By switching to Lightning for audio Apple could deliver significantly more features - as it does already with the audio accessory protocol that allows car head units to easily traverse playlists and display playing track information.
Yes, it would render the iPhone incompatible with all sorts of legacy headphones but that's hardly been a barrier to new functionality in the past. At this point I'll point you at the original iMac, which dropped both legacy ports and the floppy drive in favour of Apple's vision of the future. Latterly the MacBook Air ditched the previously indispensable optical drive.
However, I don't think that this is Apple's reason for wanting to drop the headphone socket - or at least I don't think it's the primary one.
Apple wants to make the iPhone thinner and the headphone socket is the limiting factor in doing that today. Which is why we've seen more than one patent for new headphone socket designs from the company.
This isn't a good thing. The iPhone is more than thin enough and not a particularly pleasant thing to hold in the hand sans case. Making it thinner is sure to exacerbate this problem. And, as I've mentioned before, a thinner device means less space for battery and the iPhone can ill-afford to give up any more battery runtime.