I regularly listen to audio files in Evernote on iPhone. When I get a call, or have to pause for a few minutes, Evernote does not remember where I was in the audio and usually restarts the app.
Whether it's a voice memo I recorded with the app -- or a 1-hour seminar .mp3 I've purchased -- it's more often that the audio is at least 1 hour in length. I try to listen in one sitting, but it can be difficult.
Right now, the iPhone app will crash or reset if I switch between apps or lock my phone for a few minutes -- so I usually try to write down the audio position so I can return where