Notebooks are mobile devices . Just joking.

A nice example is the simpad. The community even made
new hardware for it.

I give some links where to search for more information

http://gpe.handhelds.org/
http://opie.handhelds.org/cgi-bin/moin.cgi/
http://www.handhelds.org/geeklog/index.php
http://www.openembedded.org/
http://en.wikipedia.org/wiki/Embedded_Linux
http://www.users.on.net/~hluc/myZaurus/distros.html
http://opensimpad.org/index.php/Main_Page

Related forum
http://www.oesf.org/forums/

Another Linux for the Nokia 770/N800
Download and test it
http://www.angstrom-distribution.org/unstable/images/