Every day for five weeks, Kenneth D. O'Neill called the phone company. He dialed just before office hours and let it ring, so his call would be the first of the day.

'It got so I'd call and they'd say, 'Hi, Ken,'" he said.

O'Neill's obsession: Grabbing the new telephone number 777-7777. He hoped the seven sevens would give a business edge to Cheap Sleep Inc., his bedding stores in Wilmington and Newport.

"It will stick in people's minds," O'Neill said. "That number is so hot there's no way it could miss."

The 777 exchange opened in January, but it wasn't until May that the final four digits O'Neill wanted became available. He remembers the day: He made his regular call to Bell Atlantic Delaware from a futon convention in Minneapolis.

O'Neill expects the eye-catching number to boost his business 10 percent, when it stands out from competitors in the new phone directory.

Few take such pains to nail down a catchy number. But plenty of small businesses spend time and money trying.

"It's a marketing tool," said Barry S. Schlecker, president of Wilmington-based Network Personnel Inc. His business number is 656-5555; his home phone, 658-5555; his car phone, 540-5555.

"Everybody knows if they dial 5555, they're going to get me," he said.

Getting a custom phone number from Bell Atlantic Delaware can cost $100. Or not.

When you ask the phone company for a new number, it gives you a choice of five available numbers at no charge. If you want more choices, you pay $100 for the service.

At least you're supposed to. Phone company representatives aren't always strict about the charge, some customers say.

Or call back the next day for five new choices – still free, Bell Atlantic's Ellsworth Edwards said.

What makes a good business number? "I've probably heard 15 different explanations of what's easy to remember," said Louis J. Freedman (737-3711) of Harrington consultants Utility Audit Group Inc.

Greenville publicist Samuel L. Waltz Jr. (777-4774) favors "radar numbers," in which the last four digits read the same forward and backward.

And like a poker hand, two pairs or three of a kind can help.

It's a memory aid called "chunking," said Helene Intraub, psychology professor at the University of Delaware.

Four random numbers take up four chunks of your memory. But two pairs take up only two chunks, so they're easier to remember.

Using the letters on the keypad to spell a word makes it one chunk instead of seven. That trick has its problems, though.

Schlecker's employment firm uses 656-WORK for faxes, but that could be confused with a competitor' s 652-JOBS.

Customers may resent the tedious tapping at letters. "It just takes forever," said Joseph K. Dombroski of Brandywine Electronics Ltd. in Newport (999-9992).

But wordy phone numbers are still in demand, Freedman said.

Some entrepreneurs snap up the good ones and sell them, he said. For instance, 1 (800) INSURE is on the market for $10,000.

Cheap Sleep's O'Neill said he has already turned down three offers to buy his number – though he might lease it for the right price.

Freedman predicts a rush to stake out new vanity numbers early next year. Since nearly all 10 million 800 numbers are being used, the Federal Communications Commission will open an 888 toll-free code.

Long-distance carriers are poised to send their requests, which will be taken on a first-come, first-served basis. Schlecker asked his carrier to grab a number that spells the company name. "They'll try, but you gotta get there early," he said.

Some stumble into a good one without even trying. At the New Castle County Chamber of Commerce (737-4343), "we just got goldarn lucky," spokeswoman Margaret C. Ritsch said.

Numbers that repeat a single digit have one big drawback, Dombroski said: "Many times you get calls from 3-year-olds. ... They keep pushing the same button."