Telephone companies next month will pull the plug on their analog services in what is known as the analog-to-digital transition set by the Federal Communications Commission. While the majority of the population will not be affected, some cell phone and OnStar users could be left without service.

In 2002, the FCC voted that as of midnight on Feb. 18, 2008, cellular carriers would no longer be required to provide analog services. The commission argued in a September 2002 report that requiring carriers to continue running analog networks harms competition because of unnecessary operating costs. Carriers would prefer to use their wireless spectrum for digital technology instead of setting a portion aside for analog services, the FCC said.

Digital technologies are also known to be more efficient than analog since they use less bandwidth and they can be used to provide advanced wireless services. Newer phone models with text and instant messaging, Internet browsing, MP3 players, and integrated cameras are digital.

Most wireless phone service users, including Sprint and T-Mobile subscribers, won't be affected by the transition, often referred to as the "analog cellular sunset," because they already use digital handsets and services.

However, those who use an analog-only handset and receive services from AT&T (and former Dobson Communications), Verizon Wireless, Alltel, and U.S. Cellular, or use analog cellular radio equipment like an alarm system and an in-vehicle OnStar system, should consider switching to digital before the FCC's deadline.

The FCC mandated that carriers notify their analog users four months before shutting down analog networks and again at least 30 days before. The two largest U.S. cellular carriers, AT&T and Verizon Wireless, have been doing just that.

A year ago, Verizon Wireless started identifying subscribers with analog handsets and offering them free digital phones as part of a new service package, said the company's spokeswoman. It's an ongoing process, she said. Less than 1% of Verizon Wireless' traffic is analog, which is why the carrier chose to shut it down next month and instead focus on its digital and broadband services.

AT&T has been notifying its customers for more than 18 months through a combination of phone calls, letters, and text messages, said an AT&T spokesman. Subscribers who haven't migrated to GSM, the carrier's digital network, may qualify for a special rate plan. If a subscriber chooses to leave AT&T as a result of the change, AT&T will waive the early termination fee, the spokesman said. Alltel and U.S. Cellular couldn't be reached in time for InformationWeek's deadline.

Users likely to have a tougher time with the analog-to-digital transition are those who have installed expensive equipment in their homes, such as an alarm system, or in their vehicles, such as OnStar's communication system.

Some alarm systems use analog radio equipment and send out a wireless signal using the 800-MHz spectrum, according to the FCC. These are generally wireless alarm systems installed before spring 2006 and they make up about 1 million systems out of a total of 26 million installed alarm systems.

OnStar's communications system provides phone services, personal navigation, and emergency services through a partnership with a wireless carrier. Without an analog network, OnStar cannot provide services to subscribers with analog-only equipment, which generally applies to 2003 car models and older. As of Jan. 1, OnStar is offering services in cars that are capable of operating only on a digital cellular network, the company said in a statement.

OnStar customers must first determine if they have an analog-only, analog/digital-ready, or dual-mode (analog and digital) system. Cars with analog-only systems cannot be upgraded, whereas cars that use analog/digital-ready can. Dual-mode-equipped cars will continue to work with OnStar's services.