The iPhone is more than capable of helping you record interviews and audio on the go. In order to get the most out of it, you are going to need a decent microphone attached to it. The Rig Mic Cast is a portable voice recording microphone designed for recording podcasts, interviews, lectures and everything in between. You get two free apps (iRig Recorder and VocaLive) to do your recording and editing more easily. This will set you back $40 though.