As with all phones, I'd only do it as a last resort. For giggles, two of us took a set of CA-14s (w/ battery box) and tried with a new iphone and it sounded better than the internals, but not by much. The ADC is crap since it's not designed for this purpose so they cut corners on the cost. If there was a pre-amp that exported to micro usb, that would resolve like 3/4ths of the issues. Someone could program a capture program easily enough, but getting the signal sent via usb (without requiring real interaction which would entail drivers) would be the kicker.
On that note, there was some talk about using a USBPre2 with an ipad as long as you could provide power elsewhere since the ipad underpowers the usb devices that are connected and SD noted it as such.