People have asked I start a thread regarding recording with an iPhone.
Some may think there may be issues, but It's not as scary as it seems. One good thing is you can adjust the settings so you have to hold down 'stop' for 3 seconds to stop recording, so you don't worry as much about pressing a tiny record button twice putting the recorder back in the bag. I'm using an Apogee Duet (iOS) interface which has very good preamps and DAC in one box. You would need to power that Duet with external power such as a Lenmar DVD battery. All the converting is performed in the Apogee Duet and the iPhone is essentially a bit bucket and DAW. The breakout cables are kind of a pita in the field or even used on a desk, but it's ok. You can purchase a breakout box which may make sense in the field but I haven't used one. Recently I've been using a Sonosax SX-M2 into the Duet (line level) and just using the Duet's converters. I like it. Apogee Metarecorder is a basic free software for iPhone and I use Auria for iPad.