The information highway was filled with roadblocks as millions turned to the Internet searching for news about the worst national catastrophe since Pearl Harbor.

Cell phones and land lines failed repeatedly, overloaded by users calling family members. Cellular phone companies appealed to customers to limit all non-emergency calls and to use to land lines.

“Right now the networks are jammed,” said AT&T Wireless spokeswoman Danielle Perry.

Locally, Ameritech Corp. said it heightened security at facilities across its territory. A spokeswoman said the system was operating normally despite higher volume, but many callers reported finding busy circuits in Chicago’s 312 area code.

In the Washington D.C. area, Cingular Wireless was bringing in portable cell sites on wheels to try to alleviate the network congestion. The company reported a 400 percent increase in call attempts. “We don’t know how many of those calls have gotten through,” said spokeswoman Michele Daro.

She asked customers to wait at least 10 seconds between unsuccessful call attempts to give time for data to clear from the handset to the cell site before trying another call. “Otherwise there’s just more congestion. (The network) gets confused,” she said.

In Chicago, as people stepped off trains during the morning rush hour, they shared news by listening on their cell phones, then turning to the oldest form of communication, word of mouth, to tell fellow commuters what they had heard.

“Everybody was on their cell phones, looking up, getting information and then passing it on as fast they could,” said Lante Corp. executive assistant Barbara Miller. “It was eerie.”

Miller kept abreast of developments by listening to radio reports at her desk, while small knots of employees at Lante’s Fulton Street headquarters gathered around a television in a lobby.

“I went to go online at CNBC and couldn’t get through,” Miller said. “I got some information from CNN’s site.”

Traffic to CBS.MarketWatch.com overloaded as the site tried to deliver roughly 5,500 simultaneous video and audio streams from the site in the hours after the blast. While telephone calls produced busy signals, quick e-mail messages confirmed that loved ones were alive. E-mail and instant messaging use far less line capacity or bandwidth than news sites with photographs and streaming video or audio feeds.

“This is just a quick note in case you were wondering whether there was any chance I was in Manhattan this morning,” Fordham University doctoral student Doug Carriker wrote to family and friends. “I wasn't, but I can see the devastation and the plume of smoke covering the financial district from my rooftop. Unbelievable.”

A reporter, stepping out of a magnetic-resonance imaging tube around 10 a.m. after a one-hour test, was greeted by medical technicians who told her, “A lot has happened since you went in there.”

Tribune staff reporter Christine Tatum contributed to this report.