Sonia Levin couldn't get to the phone fast enough when she received a card in the mail from Disc Sweepstakes Ltd. congratulating her for winning one of three prizes -- a 1990 Mercedes-Benz, a Hawaiian vacation for two or a full-length mink coat.

"Call now for immediate confirmation" stated the card, with a 900 number printed underneath. Excited by her prospective winnings, Levin started dialing.

But instead of congratulations, she got a recording that said there must be some kind of mistake.

That call, which lasted less than a minute, cost Levin $9.90.

What she had failed to notice was the small print on the card that warned of the surcharge.

With that, Levin joined the ranks of the more than 800 people who have filed complaints with the Federal Communications Commission in the past year over what they claim are abuses of 900 numbers. Called "dial-it services" by the FCC, the long-distance numbers are used by a growing number of businesses, from retailers to credit card companies, offering various services. Often, the numbers are used by legitimate companies. But in recent months, the number of complaints has escalated from people who claim they were duped by companies that deceived them into calling 900 numbers with exorbitant rates.

"We see abuses in 900 numbers as a new trend in fraudulent telemarketers," said Eileen Harrington of the FCC's Bureau of Consumer Protection.

If there is a question about the actual charges, the complaint is sent to the local phone companies, since they handle the billing for the firms that use 900 numbers. If the issue is potentially false or misleading advertising, the case is passed on to the Federal Trade Commission.

So far, Harrington said, cases have been filed against two companies that provide 900 numbers -- one in Baltimore and the other in Georgia. In the Baltimore case, the FTC has charged two companies there, First Capital Financial Inc. and Midas Financial, with misleading consumers by deceptively advertising and marketing "gold card" credit cards.

According to the complaint, the companies advertised on television and in newspapers that they offer a credit card similar to gold cards issued by MasterCard, Visa or American Express but that can be used only to purchase items from catalogues distributed by the defendants.

The 900 numbers are long-distance services; 976 numbers are local services that are usually limited to only one city.

The flock to 900 lines has been dramatic and sudden. According to Chris S. Elwell, editor of Information Industry Bulletin in Connecticut, the number of 900 numbers has grown 83 percent in the first half of the year to 2,950 as of June.

Callers use 900 numbers to obtain everything from stock quotations to crossword puzzle clues to travel information. Charities employ them to raise money, and adult message services use them to deliver pornographic recordings. The fees run anywhere from 95 cents for the first minute to $99.99 in some cases.

The growth of the service has attracted the attention of legislators. Rep. Bart Gordon (D-Tenn.) of the House subcommittee on telecommunications and finance, submitted a bill last month aimed at protecting consumers from deceptive and misleading practices regarding 900 services. An oversight hearing was held Sept. 27 and a new proposal will be made next year.

Among the measures the bill calls for is better disclosure so that people will not be surprised by the price of the call. It also would require phone companies to include an introductory message that would specify clearly the total cost or per minute cost of the call and give the caller the option of hanging up at the end of the introductory message without incurring any charge.

Some people, however, question whether the legislation will adversely affect the growth of the services.

"The legislation might unnecessarily hamper the continued growth of those services and thereby deny the consumers and businesses the benefits that such services may offer," testified Richard M. Firestone, chief of the Common Carriers Bureau of the FCC, at the hearing last month.

He said that the FCC is reviewing its rules, regulations and practices regarding 900 services to determine what further steps might be needed.

"Any time you pass legislation on industry, it curbs a good side of the growth potential," said Paul Davies, director for corporate communications of Telesphere Communications Inc., one of four companies that provide 900 network services.

"Some potential legislation talks about blocking -- that's First Amendment stuff, you don't block things," he added. "Policing it makes more sense."

"Self-regulation of the industry would be more effective," said Sharon L. Lundeen, promotions and public relations administrator for Sprint Gateways, which provides 900 and other information services. Telesphere is already moving in that direction. The company has established a monitoring system to ensure that no adult programs are used on its network. "Once the program is up, we have part-time people, even ladies at home with their children, who call everyone of our programs every day to monitor them," Davies said.

Some callers are taking action of their own by refusing to pay 900 bills when they get them if they feel the charges are unfair.

Andrea C. West, American Telephone & Telegraph Co.'s national marketing manager for its Multiquest 900 system, explained that it has a 3 percent refund rate, meaning 3 percent of the 900 calls it transmits are not paid for by the callers. West said that what they do is charge the cost to the owners of the 900 numbers.

Some 900 number holders have retaliated by filing private cases against customers who refuse to pay for their calls. The FCC's Firestone said that out-of-court settlements are usually arrived at with the amount to be paid cut drastically.

In the meantime, people like Sonia Levin are encouraging an education campaign for everyone to be more aware of what they will get when calling a 900 number.