As the day wore on it became clear that, although thousands of lives had been lost, the telecommunications infrastructure in the US was essentially operational.
By the time reports told the world that the Pentagon building had been hit by a third hijacked airliner, less than an hour after the World Trade Centre attacks, officials were urging residents to stop making phone calls over both landlines and mobile phones in a bid to keep lines free for emergency calls and for those frantically trying to contact loved ones in the affected cities.
One national mobile operator reported that network call traffic surged to 400% of its normal level in the two hours after the first incident.
Many telecoms carriers, Internet service providers and network vendors put security precautions into place, closely checking employee identification cards or implementing other measures that most declined to specify.
Verizon, a local fixed-line and cellular carrier that serves both Washington and New York, said calls to the area doubled from their normal peak volumes of 115 million in New York and 35 million in Washington in the wake of the incidents.
Traffic on the cellular network was running between 50% and 100% above normal levels. Verizon's directory assistance and operator services were also overwhelmed, the company said in a statement.
The initial attack knocked out as many as 10 base station sites that used connections to land lines that went through the World Trade Centre, Verizon said.
Verizon added that most of its 488 employees who work on the lower floors of the North Tower of the World Trade Centre complex had been accounted for.
By late afternoon, major carriers, including WorldCom, were reporting that operations were running more smoothly, but under emergency procedures.
Phone traffic to the US was also disrupted with carriers responding to requests from their US counterparts to limit traffic.
Web traffic surged but the basic infrastructure held up. AOL, the world's largest ISP, and hosting company Exodus Communications are both based in Dulles, Virginia, near Washington. Both companies reported that operations were not affected despite the surge in Internet activity.
Perhaps most affected were news sites. CNN.com, part of AOL Time Warner, could only be reached sporadically after news of the tragedy spread.
The company responded by stripping graphics and links from the home page and boosting bandwidth. Within hours the site was fully accessible, as were the Web sites of other major media outlets, including those of The Washington Post and The New York Times, both of which provided frequent updates.
The spike in Internet use was, in fact, "relatively short-lived", according to Matrix.Net, a Texas-based company that measures Internet performance. IP traffic returned to "near-normal performance levels within about an hour" after the initial spike in traffic occurred.
The Internet "appears to have survived a severe test of the adaptable traffic routing concepts it embodies", the company said.