Apple has improved the camera in their iPhone with each iteration, but the microphone hadn't changed much. Sure, there's noise cancelation, but the position of the microphone is problematic, and it certainly doesn't pick up stereo audio.
Fortunately, there is the Zoom iQ5, which was just released at the NAMM tradeshow. I had access to an early unit, to test during CES and at home, and it's quite impressive. There's a lot of technology in such a compact unit. So much that I'll just quote from their release:
• High-quality mic that connects with iPhones, iPads and iPod touches
• Rotating mic element for vertical (audio) and horizontal (video) positioning
• 3-position Mid-Side stereo field switch (90°, 120°, RAW)
• Analog mic gain wheel
• Auto-gain and Limiter functions
• Connects to devices via Apple’s Lightning connector
• Mini USB connector for powering/charging iOS device
• Free Handy Recorder App available for download via the App Store
To be honest, the most common use I have for the microphone is accessing Siri. And lately, Siri hasn't been understanding my requests for directions. I tried repeatedly to find Browncroft Boulevard, and it kept replacing that with Bronco Boulevard and other non-existent locations. Maybe Siri has got the Super Bowl on her mind? I plugged in the Zoom iQ5 and it understood me just fine, on the first try.
For audio recording, say at a concert or classroom, the iQ5 really shines, as it can actually separate left and right channels, and you can adjust gain as desired. You can use your favorite apps, or checkout their free Handy Recorder app as well.
The Zoom iQ5 is novel because it plugs in to the Lightning port, so all communication is digital, not analog. That's a big plus. You might be worried that by using up the Lightning port, you cannot charge your iOS device, but a miniUSB port allows for pass through charging (iPhone and iPod touch only; iPad and iPad mini charging is not supported.) It might have been more practical to have used microUSB, but it's not a deal breaker. There's also a headphone jack since the iPhone 5's port is obstructed by the device. The Lightning connector works best with a "naked" iOS device, so if you have a bulky case, it might not have enough clearance.
The iQ5 is available in black or white, and looks like a disco ball when plugged in to your device! I almost expect it to start rotating! Technically, you can rotate it manually, 90 degrees, to switch between portrait recording or landscape video recording, for true stereo separation. If you do a lot of recording on your iPhone, you should check out the Zoom iQ5.