This should have existed, oh, the moment GPS was commercially available. Nevertheless, I'm happy to hear that an Italian company is currently testing a GPS app written specifically for the blind. It's Symbian-only right now, but I have an extremely difficult time believing a similar app couldn't be written for Windows Mobile:
It requires just two dedicated keys on the mobile phone - one which, when pressed, tells the user their exact location including the house or building number and the other one alerts the call centre that the person needs assistance with navigation.
The next stage, the call from the call center, involved being given step by step directions from a human being in real time. Funny how my initial reaction to that is distrust (how many times have you been given bad directions?) - but not being blind means you can visually look around a map to see if something's accurate. So all in all, let's hope we see this sort of thing here.