Makarand writes "According to this Mercury News article users of GM's OnStar system are finding that they can modify their OnStar unit to make it work with commercially available mapping software after disconnecting it from the OnStar network. Websites and message boards are rife with step-by-step instructions to personalize OnStar's navigational and communications components. When a driver requests directions from OnStar his GPS data is routed over an analog cellular network to OnStar computers and the directions are read back to the driver on the same network. The price for this service is around $400 each year. Those who tap into their OnStar systems pay no such fees."