vocal indication of maps not working on iPhone4

I have an iPhone 4. When I'm in the car and I use maps application (preinstalled on the phone) to get some indication, I have to stay with the eyes locked on the screen not to mistake the road.
Well, the first thing i saw on the apple web site is that they have made some accord with the car company to integrate siri in the vocal equipment of the car so you don't have to look at the telephone if you need something...and drive safely...
Isn't also safer put some vocal indication on the iPhone 4 while using maps?
I don't think i'm the only one in the world who has this model of iPhone.
I don't ask for siri, i know, the now iPhone has to have some more and better stuff than the old one...but COME ON!
I installed google maps application and they put vocal indication...i would prefer use apple maps...but like this is IMPOSSIBLE, i don't want to crash my car!