have you tried google?
mate of mine had a "thing" called route 56, it connects via bluetooth to the phone, and tells him where he is / wants to go, trouble is as the screen is his phone, its too small to be of much use.
if i needed one i would be inclined to get a satnav, although i have seen stuff for a pda, but cost i would get a sat nave (unless you have a pda)