If you own a 2004 or earlier model-year GM vehicle, come 2008, your built-in OnStar system may become obsolete. The shutdown is a result of an obscure Federal Communications Commission ruling from 2002, which allows cell phone companies to shut down their analog networks beginning in February 2008.

Analog networks were used years ago because they were the most pervasive, reliable, and offered greater coverage. Digital networks have proliferated, though, and only some pre-2004 models will be able to upgrade, leaving the rest at a lost. OnStar has not said how many of its subscribers will be affected. But Frank Viquez, an industry analyst at ABI Research, estimates as many as half of OnStar's customers, two million subscribers, now drive cars that cannot be upgraded. Verizon Wireless, the network of choice for OnStar, has not said how or when it will dismantle its analog network, though it has not ruled out shutting off the service all at once.

Even after OnStar failed to persuade F.C.C. not to phase out analog networks, the company continued to install analog-only equipment after 2002, when it was clear that a phaseout was more than likely. In a statement to the New York Times, OnStar said, "We at OnStar sincerely regret that we will not be able to provide OnStar service to vehicles with analog-only hardware after Dec. 31, 2007." OnStar's explanation as to why it continued installing analog equipment in the face of a phaseout: "Each vehicle has its own development and manufacturing schedule, and not all vehicles will receive the same OnStar equipment at the same time."

To read more about OnStar, click here.