It was once "One of the hottest open-source products around". Now it's pretty much defunct, although you can sill buy the hardware and there is some hard-core Linux support for the hardware.

OpenMoko is a project to develop a fully open-source cell phone to, in the words of founder Sean Moss-Pultz, "free your phone."

Wiki - the main info source
Buy a Neo1973 (Note they are still in "developer preview" status; consumer-ready versions expected "real soon now")
Slides from Ian's talk, given at Ontario Linux Fest, October 2007, at Toronto Asterisk Users' Group, and elsewhere (PDF, 3.2MB, Creative Commons license)

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