While doing some research on my TomTom One 3rd Edition and GeoCaching I discovered
the my little device is running Linux and appears to be very hackable. (Not that I
have anything that I really need to change on it)

http://www.opentom.org/Main_Page

http://www.opentom.org/TomTom_ONE_3rd_Edition

http://www.opentom.org/TTconsole

http://www.opentom.org/BTconsole

How to change the voice files:

http://stefans.datenbruch.de/tomtom/

Hacking the TomTom ONE through Open Source

http://www.itwire.com/content/view/13531/53/

TomTom Linux Project

http://www.slashgear.com/tomtom-linux-project-303219/