Vibrant Solutions Inc.'s software checks as many as 5 billion records a day to make sure its telecommunications carrier clients aren't overcharged.

That means tracking, among other things, the location, duration and rated price of every bit of data transmitted over the client's network.

The benefit? In some cases, a carrier can recover up to 8 percent in overpayments it never realized it made.

Money is tight in the telecommunications industry. Carriers spent billions of dollars building networks in recent years. Too many carriers built too much capacity, pushing prices down and driving many of the firms out of business. The survivors are now forced to watch their pennies, and some are finding spare change in mistakes in their billing systems.

"The drive here is to discover revenue leakage areas, which is significant in the telecommunications industry," said Verne Anton, an analyst with the Gartner Group, a market research firm. "The market is such that it is looking for these things now. This is found money."

Long-distance carriers and competitive local carriers typically pay 40 to 60 percent of their revenue to other carriers to handle their phone calls, and, on average, 3 to 8 percent of the charges are wrong, said Rich LaPerch, chief executive of Vibrant.

Auditing billing systems is immensely complex because a communications system is made up of hundreds of companies whose wireless, long-distance, local and Internet networks crisscross, ferrying one another's e-mails and calls. There are more than 200 categories of fees, taxes, tariffs and service fees that carriers charge for carrying each other's traffic. So over the course of a month, a carrier's bill for calls and Internet usage takes up reams of paper.

But the market for these services is full of competitors. Some companies develop and manage their own bill-checking systems. Consulting firms such as PricewaterhouseCoopers LLP and BearingPoint Inc. install software for many carriers. Then there are companies such as Connexn Technologies Inc. and Fairfax-based Vibrant that make the software that audits the bills.

Despite competition, Vibrant said its revenue increased 23 percent last year, and 72 percent the year before -- two years in which it also lost customers to bankruptcy.

On the other hand, cash-strapped companies are also a good audience, LaPerch said. "We have never failed to find customers money."

Vibrant formed 21/2 years ago as the result of the merger of four private companies, two of which were Telecon LLC from Fairfax and Longitude Systems Inc. of Chantilly. It is funded by venture investors, including Alexandria-based Columbia Capital LLC, Grotech Capital Group of Timonium and Bessemer Venture Partners in Wellesley Hills, Mass. Vibrant has gotten $37.5 million in two rounds of funding; it more than 30 customers and 140 employees.

Vibrant gets paid only when it recovers money for a client -- a practice that analysts say makes its service easier to sell. . Last year, Vibrant developed software that similarly audits the incoming money -- "revenue assurance," they call it -- finding typos and glitches in administrative systems that prevent companies from collecting from customers.

"As much as 3 percent of revenue could be left, literally, on the floor," LaPerch said.

Reston-based Nextel Communications Inc. saved a "significant" amount since it started using Vibrant's billing auditing software four years ago, said Audrey Schaefer, a spokeswoman for the wireless company. She declined to elaborate on the savings. "It is extremely important to Nextel to make sure we pay for only what we should pay for."

Technology that recaptures money "is one of the hottest sectors, in terms of software," said Jason Briggs, a software analyst with the Yankee Group, an industry research firm. Vibrant already faces stiff competition from many others that offer billing audits, so its challenge will be landing customers for its new revenue assurance software, he said. "It's a space everyone's looking at right now."