Last March, two OnStar customers in Pennsylvania, Robert and Sarah Gordon, sued GM for leaving analog subscribers behind. They are seeking damages and an injunction to force OnStar and GM to provide repairs or upgrades, and they want to turn the suit into a class action. It has been consolidated with a handful of other actions in the U.S. District Court for the Eastern District of Michigan.

Among cell-phone subscribers, the analog sunset is most likely to hurt so-called "glovebox users," said IDC analyst Scott Ellison. These are users, often elderly, who just keep a cell phone in the glovebox in case their cars break down. They usually don't feel a need to update their handsets.

"If you know that you have some kind of wireless link or wireless communications device and you're unsure whether you are affected, call your service provider," Ellison advised. A tip about phones: "If it has a color screen, you should be fine," he said.

AICC's Fiore gave similar advice. Some consumers have ignored potential problems with alarms because they confused the analog cellular shutdown with the end of analog TV, which won't happen until next January, he said. If you notify your alarm provider and they are prepared to go digital, all a repair person will have to do is come into your home and replace the radio, possibly moving it to another part of the house with better GSM coverage, Fiore said.

The perils of the analog shutdown point to a mismatch between technology lifecycles, IDC's Ellison said. Cars and home appliances often stick around for many years, while wireless technology changes more quickly. In fact, Illinois Valley Cellular, in rural Marseilles, Illinois, serves few analog phone users but plans to keep its analog network running after Feb. 18. That's because wind turbines that generate electricity in its service area still use AMPS radios to exchange operating data, according to Data Routing Manager Pam Craig. Replacing those radios would be difficult and expensive.

But as new technology comes along, such as cellular networks that use scarce radio spectrum more efficiently, the old often has to give way, Ellison said. As technology rapidly advances, will it happen again to wireless networks we take for granted now? "It probably will," he said.