You can buy a developer unit right now, although the list of currently incomplete features should (rightly) discourage all but the most enthusiastic.

http://www.openmoko.com/

I think when the software is more complete that this could be a great mobile phone. The idea of having almost total control over the operation of a mobile phone seems like a very clever idea.

Some ideas that came to me:

• Use the onboard GPS to perform actions when in particular locations (automatically forward calls to my home number when I’m at home for instance, or automatically switch off the phone when I’m at the cinema. Possibly  use different answer phone messages when in different places)
• Simplified user interfaces with more active assistance for people who only want a basic phone
• A system that uses the location system to look up things on google maps. (like nearby restaurants that are open and have good reviews)
• games that use the physical location as part of the gameplay. (Like a treasure hunt maybe?)
• More advanced actions when people call (like bringing up events that they are connected with, or documents they’ve sent)

These are just some ideas I thought up as I was writing this, there are probably other better ideas around. Some of these ideas have been done, but I think that the openmoko scheme has a number of advantages over other hardware.
I really want one

Although I will probably wait until the software stabilises and they add a camera. The current plans include a new hardware revision in the Autumn (with wifi) and then more models next year.