WASHINGTON - One of the hard lessons of Sept. 11, 2001, is that if another major terrorist attack were to occur, most cell phone calls in the affected area likely would not go through because of congested wireless networks.
But the rapid growth of text-messaging technology means that most cellular telephone users have a way around that problem.
Text messaging, a feature that has become nearly universal on digital cellular phones, allows users to send and receive short texts on their phones' small screens. Experts say it would be wise for cell phone owners to learn how to use the function because that may be the only way to communicate by cell phone after an attack.
Text messages are transmitted on the same networks as voice calls but tend to contain much less data and can be stored in a queue to be delivered when the congestion clears.
"They're a little bit like motorcycles during rush hour," said Travis Larson, a spokesman for the Cellular Telecommunications and Internet Association, a trade group based in Washington. "They're smaller, faster and more agile and can get by on the shoulder of the road when everything is gridlocked."
Nearly 90 percent of the phones in consumers' hands are digital, Larson said. And nearly all digital phones sold in the United States have what is called short message service, or SMS, with message length typically limited to less than 200 characters.
In an emergency, that is more than enough characters to instruct family members to "MEET AT UNCLE MIKE'S HOUSE AT 7 PM," for instance.
In addition, last summer it became possible for cell phone users to send text messages to anyone else with a digital phone. Before that, text typically could be sent only between people using the same service provider.
The greatest challenge for users may be composing messages using the phone's buttons. Because most keys have several letters, it takes practice for users to learn to tap a key once for the first letter, twice for the second, and so on.
Wireless networks are allocated only so much space on the radio spectrum they share with broadcasters and other users. So there is little extra capacity to handle spikes in call volume that can occur during large-scale emergencies such as a bad storm or a terrorist attack.
The problem exists despite expansion of cellular towers and antennas in recent years to keep up with the rapid growth in subscribers. Industry statistics indicate that on average, 50 new cell phone antenna sites are added each day.
"It's like any other public network, whether it be a network of roads, a network of wire lines or the Internet," Larson said. "No public network is designed for everyone to use at the same time."
He compared the problem to rush-hour traffic jams or the busy signals people get on Mother's Day when they try to place calls from their home telephones.
The Department of Homeland Security has acknowledged that during a crisis, wireless phones could be next to useless.
When the agency issued recommendations to Americans on preparations they should make, it advised "developing a family communications plan that specifically should take into account that cell phone coverage and possibly even regular phone coverage might not exist following a terrorist attack," said Brian Roehrkasse, an agency spokesman.
Frank James writes for the Chicago Tribune, a Tribune Publishing newspaper.