I just thought I'd post that my N9 has just developed this problem. The earphones which Nokia supplied work, and one other set, but they aren't much good for me: they don't fit my ears well and I'm a bit deaf, so I spent lots of money on a better set of Phonak earphones and an amplifier. Neither of them are recognised by the phone now, so wasted money unless I buy a separate MP3 player that works.

Unfortunately headphonefix doesn't work on my phone either, which is a terrible shame as it seemed an ideal solution. I'm not sure if I've installed it wrongly or something, I'm pretty ignorant about the phone. I just double clicked on it in the file manager, having set the phone to install non Nokia Store software. It looks as if it installed ok, but the buttons don't appear to do anything. Anyway, thanks greatly to Mitrandir for trying, and I'm glad if others have found it works. If anyone can suggest anything to get it going on my phone I would be very grateful.