When the earth started shaking, residents across the East Coast grabbed their cellphones and began calling.

But when it seemed to matter most, many got only busy signals on jammed networks.

The episode highlights Americans’ growing dependence on their wireless devices — and that technology’s shortcomings in emergencies. The inability to get a signal Tuesday echoed the frustration on Sept. 11, 2001, when residents of New York and Washington, D.C., couldn’t get through on mobile phones.

And yet, in the decade since then, the number of budget-conscious Americans who have cut the cord on traditional telephones has exploded. By last year, a quarter of American homes had replaced landlines with wireless phones, an eightfold increase since 2004, according to the Centers for Disease Control.

Tuesday’s disruption was short-lived, according to the major national carriers; Verizon Wireless said the worst of it lasted about 20 minutes. In that time, calls on old-fashioned copper-wire phones largely sailed through.

The cellular outages were “significant,” according to the Federal Communications Commission, which has been keenly aware of the number of families dumping their landlines.

“We are conducting a thorough assessment of the outages to determine appropriate next steps to improve communications services during emergencies,” the agency said in a statement.

Many consumers said they could communicate only via Web services such as Twitter and Facebook.

The earthquake didn’t appear to damage cell towers. They simply got jammed because everyone tried to call at the same time — a problem exacerbated during times of emergency. Voice calls take up more bandwidth than texts and e-mails, which carriers have urged customers to use instead.

“The industry’s infrastructure appears to be intact, but because many wireless consumers are using the networks, we are experiencing higher than normal traffic,” said Amy Storey, a spokeswoman for the wireless trade organization CTIA. “In these high-volume instances, there can be delays.”

Public safety responders in the District and Prince George’s, Fairfax and Arlington counties said they used radios to communicate with no problems and do not rely on cellphones.

The FCC, which oversees public safety communications, was ordered by Congress after 9/11 to create a dedicated network for fire and rescue departments and police to coordinate during times of emergency. But despite several proposals, the efforts have been stalled in Congress as public safety groups and carriers squabble over scarce airwaves.

For many, the earthquake was a reminder of the usefulness of plain old telephones.

Tim Wilkinson, 47, was sitting in his ground-floor office in Charlottesville when the building began to shake and he used his office landline to reach his daughter, a student at the local community college, on her Verizon cellphone. His phone worked, but hers didn’t. At first, he got a busy signal. After a few tries, he got through. His wife called his office phone from the family’s landline at home without a problem.

Wilkinson said he has kept his landline despite having two cellphones for just such occasions. Coverage in their home is often spotty, so cutting the cord was never an option.

“We’ve seen cells go out down here from hurricanes, snow, etc.,” he said. “Our landline has always stayed on.”

Others turned to Web-based calling services such as Skype or social networks to tell family and friends how they were doing. Facebook said that by late afternoon, the word “earthquake” appeared 3 million times in status updates.

Eric Scott, 24, turned to the social networking site when his cellphone let him down. He got error messages or simply silence each time he tried to call his mother in Northeast Washington using his T-Mobile Droid. He said his cell service was down for a half-hour after the quake, and he had not received any text messages two hours later.


To which a friend replied, “Social media starts revolutions and riots, and now saves the day!”

At the University of Maryland, officials warned students and faculty through e-mails and text messages that the cellular airwaves could quickly become clogged.

“Cell phone use is limited. Limit calls to police for emergencies only,” the message said.

Emergency call centers also reported becoming overwhelmed with residents checking in and reporting the earthquake. U.S. Park Police and Prince William County Police turned to Twitter to urge people to limit 911 calls unless they were truly in danger.

“Tune into local news for info,” the Prince William Police department tweeted.