Some longtime employees of North Pittsburgh Telephone Co. still have trouble getting used to the quiet.

Much of the company's headquarters on Gibsonia Road in Richland used to be filled with banks of stepper switches, noisy electromechanical devices that made and broke connections each time one of the company's thousands of customers dialed one digit in a phone number.

What was high technology in the middle of the past century was replaced by electronic switches in 1976 and by digital switches today that put through calls in near silence.

North Pittsburgh, founded in 1906, is marking its 100th birthday this year. Since 1985, the local phone-service provider has been one of three operating units in North Pittsburgh Systems Inc., a telecommunications company that also offers a variety of business and Internet services.

"We are not on the 'bleeding edge' of technology, but we have been quick to adopt things once they have been proven to work properly," said N.W. Barthlow, North Pittsburgh Systems' vice president and secretary. "Our customers expect the latest technology."

The company began with a turn-of-the-century push to take advantage of a new invention. A group of farmers, business people and community leaders living in the rural area where Butler and Allegheny counties come together asked the Central District Printing and Telegraph Co., which provided Pittsburgh with phone service, to expand north. The forerunner of what is now Verizon declined. But the utility offered to allow a local phone company to connect to its long-distance lines, according to a corporate history written by Jerry D. Johnston. Mr. Johnston is North Pittsburgh's public affairs and advertising administrator.

The new company was chartered Nov. 1, 1906, with R.M. Gibson as president and general manager. In 1908, the company issued its first annual report. It had installed 258 phones across a sprawling area that covered 11 townships. The company reported $4,274 in revenues and $6,095 in debts. Its expenses included $2,419 to buy phones and a switchboard and $125 to compensate William A. Denny "for damage to a colt."

Over the decades, the company expanded its service area, acquiring People's Telephone Co.'s lines and phones in Mars in 1923. It bought Saxonburg Telephone Co. in 1953 and Freeport Telephone and Telegraph a year later.

Starting as early as 1917 -- when the company replaced the horse and wagon its linemen used to maintain the phone system with a Model T truck -- the company has been quick to acquire new equipment.

A 1950 photograph from the Pittsburgh Sun-Telegraph shows general manager R.F. McKelvey and plant superintendent K.O. Graves demonstrating how North Pittsburgh customers now could dial Harrisburg and Philadelphia directly.

Another photograph in the company's archives shows construction in 1954 of a microwave tower behind the company headquarters. That year, North Pittsburgh became the first independent company in the state to use microwaves as a backup system for transmission of telephone calls, according to Mr. Johnston.

The company also moved into related businesses. North Pittsburgh had been selling supplies and equipment to other independent phone companies, and in 1979 created its PennTelecom unit, which provides a variety of communications services and has its headquarters on Rochester Road in Cranberry.

In 1985, the company restructured and created North Pittsburgh Systems Inc., a holding company that separated its highly regulated utility business, North Pittsburgh Telephone, from PennTelecom and Nauticom. Nauticom is the company's Internet service provider, Web host and consulting arm.

North Pittsburgh Systems has about 450 employees, and it had revenues of more than $100 million in 2004. Its companies provide more than 130,000 lines to residential and business customers. Its shares trade on the Nasdaq market under the symbol NPSI.

The company's Richland headquarters is a complex of interconnected structures built and remodeled over the past half-century. Departments and equipment have come and gone as the company has had to react to rapidly changing markets for telephone and other communications services.

Most installers and line maintenance employees work from the Richland headquarters. The walls outside the purchasing department are lined with examples of the clamps, hand tools, cable, circuit boards and phone jacks that are available from the company storeroom. "We don't use too many of those," said purchasing manager Joe Buck, pointing to a 6-inch ceramic insulator. That insulator, however, would have looked familiar to Charles Crawford and John Forsythe, the company's first two linemen.

The new heart of the North Pittsburgh Telephone's system is the DMS 100. It is made up of banks of digital switches enclosed in tall green cases that route thousands of phone calls in an instant.

Mr. Johnston offered one example of how much computing power and information could be contained in that room. He pointed to one blue cabinet about the size of a large refrigerator. That unit, he said, handles voice mail for all of the telephone company's customers.

The noisiest part of the building might be the customer service center, still decorated with black and gold signs and balloons left over from a pre-Super Bowl pep rally. Even there the loudest sound was the murmur of voices answering telephones. An electronic sign keeps track of how many sales associates are available to answer new calls.

"We try to keep our customer service at a high level," Mr. Barthlow said. "This is a competitive business, and one of the things that distinguishes us is that we have live people available to talk."

"There used to be walls around industries like ours," he said. "They no longer exist, as the lines have blurred between telephone companies and Internet service providers and [competitive local exchange carriers]."

Many of North Pittsburgh's residential customers work in Pittsburgh and know what communications services are available there. They expect their local phone company to offer the same kinds of packages at competitive prices, said N.T. Carpenter, North Pittsburgh's customer service manager. "Customers want all the bells and whistles, and they want them at the lowest price," he said.

Cellular phones, which operate without lines by transmitting their signals from tower to tower, may offer one of the biggest challenges to traditional phone companies.

Mr. Barthlow, however, predicted that companies such as North Pittsburgh would hold their place.

"We can provide high-speed broadband and that can't be delivered over cellular lines," he said. "And most people want to have a phone at home where callers can reach the whole family."

As it has for 100 years, he said, the company will continue to react to and anticipate the changing needs of its customers.