The first time I drove using the new OnStar Turn-By-Turn Navigation System, I was struck by the absence of a moving map display. I got over it—sort of. With this seventh-generation system, OnStar turned the power of technology loose on behalf of simplicity, but it doesn't have the longest features checklist.

Currently, no-frills OnStar is priced at about $10 a month; it calls for help if there's an accident but offers no navigational assistance. $30 a month includes directions read off by the always-connected operator. The way this works now, you press the Phone button on the rearview mirror and ask for directions, and the operator stays with you as long as the trip takes. This may be comforting, but it also costs OnStar a ton of money.

With OnStar Turn-by-Turn, once the operator downloads the route instructions to your car, it works just like any other nav system—except there's no map. As you approach a turn, a voice prompt tells you how close you are to the turn and in which direction (left, right, bear right, and so on) you need to turn. Two beeps indicate you're at the turn.

Most cars will have a rudimentary text display indicating the distance to the turn and the street you're turning onto. But a prototype Cadillac STS system I tested didn't have an arrow indicating whether the turn was left or right. And if you go off course and opt to have OnStar navigate you back on course, you get cryptic messages—to drive south and then make a turn, for example, leaving it for you to figure out which direction is south.

Three cars are implementing Turn-by-Turn this spring: the Buick Lucerne and Cadillac DTS now, and the sportier Cadillac STS a bit later. Virtually the entire 2007 GM line will have the new OnStar system—or more accurately, the buyer will have the option and decide whether or not to pay for it. OnStar Turn-by-Turn Navigation is included as part of the standard OnStar service for the first year on the Lucerne and Cadillac DTS and STS for the 2006 model year; extended pricing has not yet been announced. OnStar has said it expects pricing would not be different from what others charge for downloadable nav help from, say, cell phones, which is around $10 a month.

Despite some obvious issues, such as the lack of a moving map and the inability to use Turn-by-Turn to set up trips for you on a built-in nav system, I'd say that Turn-by-Turn is a nice leap forward, which OnStar accomplished by applying modest, low-key technology.