NEW YORK — The network that launched the U.S. wireless industry with brick-sized — and brick-heavy — cell phones 24 years ago will switch off in most of the country next year, leaving a surprising number of users in the lurch.

Older OnStar systems for cars, home alarms and up to a million cell phones will lose service starting in February under a 2002 federal decision that allows carriers to switch the spectrum over from analog to digital technologies, which would use it more efficiently.

The shutdown has caught some customers by surprise, including some owners of the approximately 500,000 cars whose handsfree emergency OnStar service can’t be upgraded to digital.

Adele Rothman of Scarsdale, N.Y., who said she bought her teenage son a new Saab in 2003 specifically for its OnStar, had no idea the car’s system would stop working in five years. But General Motors Corp., which owns OnStar, did — and it knew the system would be impossible to upgrade, like many others of model year 2004 and older.

Rothman, who learned in March of the impending shutdown, said she might not have bought the car if she’d known what GM did.

“I don’t think so. Not for a 16-year-old,” Rothman said.

When she complained, GM sent a $500 coupon toward the purchase of a new car.

“I was really upset because that was my tieline to him,” Rothman said. “When a 20-year-old leaves the driveway, you want to feel a little secure.”

Verizon Wireless, AT&T; Inc. and Alltel Corp. are the largest carriers that still have analog networks. Alltel will take more time than Verizon and AT&T; to close its network, shutting down in three stages ending in September. Each carrier will keep its portion of the newly available spectrum.

A few rural cellular providers may keep their networks up. Plateau Wireless, which provides service in eastern New Mexico and western Texas, will maintain its analog network alongside a digital one “for the foreseeable future,” according to Chief Executive Tom Phelps.

Many of the company’s 75,000 customers are farmers and ranchers, and the network’s superior range helps them because it fills gaps in the digital network. The larger carriers say their digital buildout will cover any gaps left by the demise of analog service.

Commercial service on the analog network, also known as the Advanced Mobile Phone Service, or AMPS, began in 1983; it was the first time coverage areas were divided into smaller areas known as cells, a move that boosted call capacity tremendously and made the modern wireless industry possible.

Even after 2002, the analog network still had the widest range, so analog wireless functions were built into millions of devices from automated meter readers, to irrigation controls and truck-tracking systems. Devices like this are the ones that will be most affected by the shutdown, while cell phones are cheap and easy to replace.

The consumer products most affected by the analog sunset, aside from cars, are home alarms. The Alarm Industry Communications Committee surveyed member companies after the Federal Communications Commission’s 2002 decision and found that just under a million home alarm systems used analog cellular to communicate with alarm centers. For most, the cellular link was a backup to a landline, but for 138,000 homes, the analog network was the only link to an alarm center.

The AICC doesn’t know how many systems have been converted since then, said Chairman Louis Fiore, but he believes 400,000 systems still use analog service, most as a backup.

“The larger (alarm) companies are in pretty good shape. There are so many smaller companies out there that are probably, I’d say, in denial. They just don’t know about it,” Fiore said.

To complicate things, some alarm systems advertised as “digital” actually use a digital subchannel of the analog network. True digital alarm system modems did not become available until 2006, according to the AICC.

According to the FCC, many analog alarms that have not been replaced by the time the network is shut down will start beeping to warn that they’ve lost the connection to the alarm center.

The Central Station Alarm Association, an alarm industry group and the parent of the AICC, tried unsuccessfully to get the FCC to delay the analog sunset.

Rapid development in the field means a faster, better technology always lurks just around the corner tempting carriers to upgrade — raising the prospect that future digital technologies will have even shorter lifespans than the analog network.

“If you’ve got a product that’s going into the market for five years, for 10 years, for 15 years, how do you pick a technology that’s going to be around that long?” asked Chris Purpura, senior vice president of marketing at Aeris Communications.

Aeris, in San Jose, runs a control center that manages automated wireless communications for alarm companies, trucking fleets, manufacturers and utilities. As late as last year, more than a million of its clients’ devices, like remote-readable electricity meters and refrigerated shipping containers, used the analog network.

Purpura said the next generation of wireless devices could be 10 times as big, making the challenge of the next transition even greater. He said GPRS, or General Packet Radio Service, could be the next network to go, since this relatively slow second-generation digital technology isn’t compatible with newer cellular broadband networks.

“I don’t think anyone wants to go through this again in five years,” Purpura said.