The current controversy involving the National Security Agency relates to cases in which domestic eavesdropping is done without a warrant.

Although the NSA is a supersecret agency, it is widely believed that the NSA has its own resources for information gathering that don't involve relying on carriers. For example, the NSA has its own satellites and other types of eavesdropping equipment that it can use to intercept communications across the air and over the wire.

As to the question of whether service providers are complying with law enforcement requests for warrantless wiretaps, none of the major service providers would comment, but the Electronic Frontier Foundation filed suit against AT&T on Jan. 31 over AT&T's alleged participation in what the EFF is calling illegal NSA wiretaps. The EFF charges that AT&T violated the law and the privacy of its customers.

In fact, the EFF suit charges that AT&T gave the NSA access to AT&T's 312TB database of call records going back to 2001 and to its database of Internet traffic data dating to 2003. AT&T has declined to comment on the suit.

Security experts say it is in the carrier's best interest to cooperate even in warrantless interceptions, because of the damage that could come to their lines from non-experienced personnel trying to tap in.

"As a practical business matter, they'd want to assist law enforcement to avoid risk to their cables or degradation in performance to the network. They'd want to be involved in anything that has to do with their connections," says one security expert, who requested anonymity.