Yeah, forget it
Or better still, when you figure it out tell the rest of us!
We aren't given access to the serial port outside of xcode NSlog statements.
The protocol for iPod control has been figured out but that doesn't help
anyone connect an external GPS or serial barcode scanner, etc.
There are a couple of apps that use a serial port with a special cable.
One is called "Get Console", and the other is an astronomy App that can use
a serial cable to control a telescope.
Both of these cables have a microcontroller in them to tell iOS that they are
authorised to allow their associated App to use the serial port, but even though
the cables are the same, the chip inside them that identifies itself to iOS
will only work with the App it's intended for,
So you'd need to buy two identical serial cable hardware to use both Apps
just because the microcontrollers in them have some different keys.
iOS is aware of either of these cables being connected.
Both of them come up in the iOS settings menu when they are connected.
Actually, it's not a huge mystery, you just have to be enrolled in the right programs for Apple to let you know how to use it. The standard iOS developer program isn't enough - you need to be in the Made for iOS program.
I could explain how everything works, but then I'd be violating an NDA.