As a little girl back in the '50s, Lilli Steinberg was enthralled by TV's The Millionaire. The sight of Michael Anthony giving strangers checks for a million bucks each week got her brain circuits a-humming. Making folks happy with unexpected loot seemed like a pretty good line to get into, she thought.

So she got into it. As president of Telecommunication Resources, the Nanuet, N.Y., firm she founded 12 years ago, Steinberg spends her time these days tracking down phone company overcharges for more than 800 corporate clients. "Four out of six phone bills have errors," says the 41-year-old mother of two, who last year recovered $5 million in refunds for her clients. "Billing procedures are too complicated for the average person. I'm like a detective, always looking for loopholes."

Her customers, all of whom have monthly bills exceeding $5,000, simply authorize access to their telephone accounts, then sit back and wait. They don't pay a penny unless they get a refund; if there is one, Steinberg keeps half. There are hundreds of possible errors that phone companies regularly make, claims Steinberg, noting that her clients average $15,000 in refunds each year.

A former high-school math teacher, Steinberg discovered the fallibility of telephone companies while working as a phone equipment salesperson back in the '70s. When it came time for billing, she says, "I saw mistakes in almost all cases." Setting up shop in her one-bedroom Manhattan apartment, Steinberg watched her fledgling business boom after Ma Bell's breakup in 1984. With her clients suddenly receiving up to 15 separate bills each month—for 800 numbers, long distance calls, equipment, etc.—paperwork increased tenfold. Often, so did the number of errors.

Steinberg hopes to open offices in Canada and Europe soon and to expand her staff of 20 employees. One bill they won't be scrutinizing, however, is the one for Steinberg's home phone. "I never get a refund for myself," she admits. "I can't be bothered."