OnStar costs between $17 to $70 a month. Adding navigation (called "turn-by-turn") to the basic service costs over $34 a month. CR, though, discovered that over 50 percent who used the service ...

This service, however, does not input the directions into your screen-based nav system, but instead uses OnStar's Turn-by-Turn voice navigation to guide you. Finally, OnStar subscribers with ...