In five years, consumers will pay for subway rides, soft drinks, and airline tickets by swiping their cellular telephones. Touch screens will completely replace cashiers at retail outlets. Buttons in cars will automatically download music ordered online, and groceries will show up on doorsteps based on past shopping patterns.

“The credit card may be replaced by cell phones or fingerprints and we will be living digitally in ways that are not imagined yet,” the president of the eastern region for online advertising agency Avenue A–Razorfish, Bob Lord, said. “It’s exciting because the world is changing so quickly and people are inventing things all the time.”

Avenue A is a leading online consultancy that helps companies digitize their messages to promote, educate, and sell products and services to consumers.

Ad Age calls it the world’s largest interactive agency. The firm is a division of technology company aQuantive Inc., which is listed on NASDAQ.

Avenue A’s 1,500 employees are located in 12 American cities and three foreign countries. The New York office is growing fastest with 66 new professionals added to its ranks so far this year and plans next month to move into bigger Times Square premises.

Its NY-based clients include TIAACREF, Maybelline, Polo Ralph Lauren, Starwood Hotels, Capital One, and JP Morgan Chase.

“Business is phenomenal and the consumer is pushing us faster than the organizations we work for,” he said. “We only do online. Offline has done a great job generating big ideas and 30-second commercials. Online is about helping to establish brands and to encourage two-way communication.”

Avenue A research shows that senior citizens are expected to become the fastest-growing segment of online users. One-third of the senior population is online, and by 2010, half of this group will be on the Internet. In four years, 87% of teenagers will be online.

But the biggest difference is the fact that teens are comfortable buying products online; older people are reluctant to give their credit card information.

“Sites catering to that age group must emphasize that encryption will protect them,” said Mr. Lord.

Besides building Web sites that people can buy things from, Avenue A also educates and entertains consumers with its content. Projects for Ford Motor Co., Kodak, and Mercedes-Benz are cases in point.

Ford’s emphasis has been on innovation and a visit to its Web site displays its president talking about the topic, much as he does on television commercials. But consumers can then visit a linked Web site that Avenue A created, which allows them to hone in on beautifully animated information about Ford’s engines, fuel efficiency, designs, and hybrids.

There is also a driving game that I found to be quite entertaining — I even e-mailed some of my friends and told them about it.

“The TV commercial points to a Web site that’s flat, so we created an experience to reinforce the brand,” said Mr. Lord.

Another project was for the Mercedes-Benz specialty brand AMG, which manufactures limited edition cars costing between $100,000 to $300,000. People reading online publications about high-performance cars merely click on the AMG Mercedes advertisement and start an animated experience lasting several minutes.

“They wanted to create an immersive brand experience, so the click sets up a trip to the factory in Germany,” he said. “The viewer can select the car, its options, and colors.”

New software techniques enable these unique online content/commercials and have helped Avenue A become the largest single buyer of Web advertising on press sites and on Google.