I second using Navit. I've used it on a FrankenPre 2, Veer, and Pre 3. It works great and you can set it as your default map application. There's a plugin you can install as well to start navigation from Just Type.
You can change the measurements to US instead of metric if you'd like. I haven't figured out how to turn off the voice though.
I have muted sound by just tapping the speaker icon in the right hand corner, mutes the sound and voice.
Sent from either my Pre, Pre≤, Pre≥, or TP's.*