Along the lines of the textual interface client for the blind...
If you've got this little machine working away for you, why not add a very powerful RFID reader. Add RFID tags to every new street and construction sign that have an ID and a typecode describing the message on the sign.
In the initial phase, the personal client would simply read the messages, ignoring, for instance, the speed signs, but notifying the user of construction signs and the like that may indicate danger, and of informational signs (which would give information about location).
Later on you could imagine the commercial sector adding support, putting the RFID tags in sale signs (you'd have to make it easy to write/rewrite the tags) so that the user could switch on "commercial" information and hear what sales are on in the store in front of them.
Anywho, just a thought.