Truly, this is an essential question that we need to get answered as quickly as possible. Not only do we need to know if the iPhone's audio output would work (presumably using an assortment of plastic-shrouded strands of copper and small plugs to link the two together), we need to know if Steve Jobs has been secretly working with Scott to allow the iPhone to call the 990 and issue instructions to it.
On a less silly note, I wonder how the headphone output of the iPhone compares to that of the iPods? I've always heard that it was just sort of so-so and the line output a bit better, which would match with my limited experience (I used my iPod's headphone output with the 990 just a couple of times).