"If we see attendance at 2 million or below, people will have a great experience on our network, but if there are more than 2 million, then they may see delays in calls and delivery of [text messages] with dropped or blocked calls ... The general public should be prepared for some disruption."

However, Taylor said even if the crowds reach 4 million and an emergency occurs, first responders will get priority for their wireless communications over the general public. That policy is followed by all the major carriers, he said, although Sprint also operates a separate iDEN network with Nextel service, which is heavily used by first responders and bypasses the GSM network of AT&T and the CDMA services of Sprint and .

But Taylor said that physical space along the parade route and at the National Mall only allow for about 1.5 million people, which would push spectators into other neighborhoods and onto other cell sites to help increase network capacity. Another factor limiting the crowd size is that Washington only has 90,000 hotel rooms.

The carriers are beefing up network capacity with the kind of equipment used to prepare for hurricanes and large crowd events. These include Cell on Wheels (COW, Cell on Light Truck (COLT) and other equipment to boost a cell site's capacity.

Sprint has increased the capacity of its CDMA network in the downtown Washington area by 40% and its iDEN network by 90%, while AT&T has increased capacity in its 3G GSM network by 80% and its 2G GSM network by 69%. Verizon Wireless is part of Verizon Communications which operates local phone service in the Washington area, and is expected to make similar boosts in capacity, CTIA officials said.