Earlier today I came across an excellent bit of wizardry by Rasmus Andersson called PeerTalk. It's a Objective-C library allowing you to communicate between your iPhone and your Mac over the USB dock cable using TCP sockets.
My immediate thought was that if this really only depended on having USB host mode capability at the far end, the same mechanism should be able to be used to talk to something like the BeagleBone, or the Raspberry Pi, not just your Mac. This would allow you connect your phone directly to the micro controller board and to drive hardware directly, a lot like the Redpark cable but bypassing Apple's External Accessory framework.
Yup, this is going to be useful...
So I started digging around inside the source code to see if it depended on anything that was going to be specific to OS X, it became apparent that PeerTalk was mostly some really nice socket code sitting on top of the USB Multiplex Daemon (usbmuxd). This bit of software is in charge of talking to your iPhone over USB and coordinating access to its services by other applications. Effectively this is what iTunes and Xcode use to talk to your phone when you plug it into your Mac's USB port.
So any device that wants to talk to the iPhone using this method needs usbmuxd. Fortunately for me there are a number of people that have worked oout how to talk to the iPhone from Linux, and there is a working usbmuxd for Linux.
As well as a few other dependences which aren't present on the stock Ångström Linux distribution on my BeagleBone, or even packages via opkg, building usbmuxd on my BeagleBone requires libusb and cmake. So before building usbmuxd, I had to build cmake, which meant resolving some problems with the stock compression libraries that shipped with Ångström.
However several hours later. after enough waiting around for software to build to convince me that before doing any serious development on the BeagleBone I really had to build an ARMv7 toolchain on my Mac to cross-compile things instead of building them directly on the board....
The iPhone talking directly to my BeagleBone using PeerTalk
...I managed to get a simple "hello" from my iPhone to the BeagleBone and then via screen to my Mac using port forwarding and that old stand by, telnet.
While I was hacking away on getting this working, I wasn't alone. David House was looking down some of the same back alleyways to get PeerTalk talking to his Raspberry Pi, and we batted the problem back and forth on Twitter while waiting for code to compile well into the night...
The next step is to put together a client on the BeagleBone sitting on top of usbmuxd that'll talk natively to the PeerTalk on iOS. Since I've got the source code of both ends, this isn't going to be too hard. I'll probably put something together in Python.