I have not ever heard of any laws against a GPS, Since cars have them, why would you think they would be illegal ?
For a mount for your blackberry, look to " Ram Mounts " they have all kinds of stuff. I bought 2 from them ( 1 for car and 1 for bike ) for my Garmin . They are a little higher than some , but after I got mine I was well satisfied with the quality of their products .

Rat