I have recorded a few interviews recently using my iPhone and its built-in voice memo application. I sent them away for transcription (I’ve found a couple of ways of getting this done online for about $30-60/hour of recording) but the quality wasn’t that great for the typist. However, I think I’ve found the answer: the Exeze MM1 Mini Microphone. It plugs into the headphone socket and it increases the sensitivity of the recording significantly. In tests, I can actually see the sound level needle flicker up and down, which it did not do with the built-in mic. It’s very portable and easy to use – just plug it in. Highly recommended for just under £6.