I purchased this adapter from Amazon:
http://www.amazon.com/Headset-Adapte...5144233&sr=8-1
It works, but the audio quality leaves something to be desired. I noticed there was something that bothered me, but I couldn't put my finger on it. I then carefully listened to the same track on the phone with the adapter and on an MP3 player. Things which should be pretty prominent and in the right ear are a bit indistinct and in the left ear instead. I tried the included huge "as big as the phone itself" multi-adapter included in the phone's box and it works perfectly - the output is like the MP3 player.
So now I'm on the hunt for an adapter which is compact (like the one I bought) but also doesn't introduce interference.