Cingular, the largest U.S. wireless service, said it was  suffering network disruptions in New Orleans and Baton Rouge,  Louisiana, as well as in Mississippi.

Verizon said in New Orleans, many cell sites were out of  service, limiting customers' ability to place or receive calls.  The company said customers who evacuated may be able to place  calls but not receive calls, and mobile-to-mobile calling might  also be available to some customers.

Sprint Nextel, the No. 3 U.S. mobile service, said it was  having its worst network problems in New Orleans, where callers  were unable to make long distance calls outside the city, where  it keeps key network equipment that handles calls from the  surrounding regions.

"Customers will see issues making long distance or wireless  calls within the area hit by the hurricane due to power outages  and flooding," said Sprint Nextel spokesman Charles  Fleckenstein.

Cellular services rely on towers to send and receive  signals from customers' cellular phones. Both companies said  many of their towers were running on backup power, but flooding  was hampering their efforts to reach some sites.

Sprint Nextel and Cingular said they were prepared to use  truck-mounted cellular towers to bolster service in areas where  they couldn't reach their equipment due to flooding.

Several Internet posters said telephone service of any kind  in the affected areas was intermittent, but a few found text  messages could get through to cell phones where regular voice  calls could not.