Hack a Day has a short and sweet video of Linux 2.6 loading on an Apple iPhone. Very rudimentary stuff at the moment, but the door has been pried open...
iPhone Linux - Hack a Day
The iphone-dev team has created a new bootloader called OpeniBoot. The bootloader lets you boot into a Linux console, which you can talk to over a USB serial device. They’ve got busybox working, but there is no touchscreen support yet.