Officials for Verizon said that the charges for the service, introduced four years ago, had been approved by public utilities commissions in six states and the District of Columbia and were based on the costs of converting the 555 number into a routable 10-digit number. They said Verizon recommends the 1-800 number as an alternative to 555, which they described as a ''select, elite'' product.

Al Novell, a manager in Verizon's federal regulatory group, said the clamor for inexpensive 555 service ignored technological complexities. ''People have been coming to us over the past year or so and saying: 'Do this for me. It's easy. It's inexpensive.' But it isn't.'' Mr. Novell said a national 555 system would require broad application of Advanced Intelligent Network, which adds new services to existing switches, and would cost Verizon at least $108 million.

Leo A. Wrobel, chief executive of Premiere Network Services of DeSoto, Tex., said the Baby Bells had exaggerated the costs and difficulties in an effort ''to keep this off the market.'' His company has tried to deploy national 555 service, he said, but ''Bell deliberately installed blocks.'' Mr. Wrobel's company has filed several related complaints with the F.C.C.

He compared the practice, used by several large carriers, of routing all 555 numbers to directory assistance and billing the caller for them to ''hijacking.''

Mr. Wrobel said that Premiere had activated about 200 of the 555 numbers nationally through a dial-around service, using software for the necessary conversions. ''We did it in a day and a half,'' he said. While 17-digit dial-around numbers defeat the purpose of 555 numbers, Mr. Wrobel said, they protect the numbers from reclamation by the telecommunications industry by placing them in service.

Since an aborted move several years ago, the industry has made no effort to reclaim the numbers. Meanwhile, the numbers, if activated, would be more valuable than ever, as perhaps the last seven-digit numbers in the United States. The F.C.C. exempted 555 national numbers in 1999 from mandatory 10- or 11-digit dialing in areas like Maryland and, recently, New York City, where even local numbers must otherwise now be dialed that way. (State utility commissions, however, can still require area codes with 555.)

And the numbers still work in movies and television shows, although when real-life assignments began nine years ago, only 100 numbers, from 555-0100 to 555-0199, were reserved for fiction. Recent films do not always heed the limits, but does it really matter if the cellphone number for Vin Diesel's character in the 2001 film ''The Fast and the Furious'' (555-6439) is actually assigned to Katrina Contee of Maryland? Only one of them, the movie character, can afford to put it into service.