I've looked at Voice Access, and pardon me if I have misunderstood, but it just seems to be a way of making your mobile, as it is, react to voice commands. not specifically for mobile Sat Nav apps. But I am perfectly aware that I know s0d all about mobiles.
So I looked elsewhere on the web for voice "commanded" Sat navs and they seem to be a very mixed bunch. AND only built in ones.
Also lots of people saying previously good mobile apps aren't as good as they used to be.
And of course lots of opposing comments.
BUT!!!!
Guess what, some (one assumes) TomToms can be controlled by voice command!!
click on this no tso obvious link below!
Don't know if ours do this but if they do I@ll be well chuffed!
Will check soonish!!