I'd love to be able to mod the iPhone tcp/ip stack to route packets over the accessory port either serial or better yet USB or Firewire...
The applications I'm researching wouldn't be able to use WiFi, 3G or bluetooth... Custom apps could be written to use the serial port available via the accessory port, but it would be nice to support generic apps that need network access.
I haven't tracked down much info relating to this, anyone have thoughts??
About the only way this could work would be to Jailbreak the device, and do some quite low level hacking. OS X supports NKEs (Network Kernel Extensions) that would allow you to introduce a new network interface. I don't know if the iPhone OS has these (as there's obviously not much information on it - it's supposed to be a black box). Even if it did, you'd have to make your KE lie and claim to be e.g. the Wifi device, as many applications will probe for network availability by searching for the Wifi interface.
Basically, I think this is an untenable idea. You can use the External Accessory APIs to allow your custom apps to use your dongle as a network service provider, but you can't use it to provide a new network interface. If you want this kind of open, extensible platform, then the iPhone is not really the right platform.