It's an open source phone. Here's the inevitable iPhone comparison:

The openmoko phone:

* has no built-in wi-fi
* has built-in GPS
* is cheaper
* is more expandable (battery, miniSD card)
* has a slower CPU
* has no camera
* is unlocked (you can use any GSM network; not just AT&T)
* comes with a stylus that is also a pen, laser pointer, and flashlight (via linuxjournal.com)

Open & hack-able, GPS, touchscreen, GSM, GPRS, soon with MicroSD and 802.11g - this is what the iPhone should have been. :)