In what must be one of the most unnecessarily complicated hacks in iPhone history, a couple of brainy engineers at Perceptive Development have devised a way to connect an infrared keyboard to an iPhone using a 1200 baud modem that connects to the iPhone via the headphone port.
Yeah, my head almost exploded too. But it makes sense once it's explained—well, kind of. See, while there are several ways to get input into the iPhone (the dock connector, Bluetooth, WiFi), these ports are inaccessible via Apple's 2.0 SDK. The audio port, however, is ideal for simple, low-speed bidirectional communication with cheap components, and it's accessible with the SDK.
So, for less than $20, these crafty engineers whipped up a circuit that talks to the iPhone using frequency shift keying, the same method used by some of the first modems. This modem was then modified to accept input from infrared and USB-connected devices, allowing the use of a keyboard to communicate. Finally, a 2.0 SDK-compliant terminal app enables text input. The result: a keyboard for your iPhone with no jailbreaking required!
It might not be the most graceful solution, but it gets the job done. You can geek out on a video of this keyboard in action after the break.