As PocketNow noted in their Windows Phone Mango preview, the new and much anticipated turn-by-turn feature in Bing Maps has a big asterisks that most people are probably not aware of – it requires constant tapping of the screen to activate voice guidance of the next turn.
Restrictions on your use: We do have some restrictions on your use of the service. You may not:
– present or alert an end user to individual maneuvers of a route in any way that is synchronized with the end-user’s sensor-based position along the route, (e.g. “real-time” navigation);
Until then, the workaround the Windows Phone team has implemented is simple and effective. Tap the screen anywhere to hear the next turn. Audio alerts will also prompt when you’ve made a correct and incorrect turn. Having said that, users should still be wary of local traffic laws which may disallow any interactions with the device while driving.