“Based on current trends, total bandwidth in the AT&T network will increase by four times over the next three years,” the company said in a statement.

All three companies say that placing caps on broadband use will ensure fair access for all users.

Internet metering is a throwback to the days of dial-up service, but at a time when video and interactive games are becoming popular, the experiments could have huge implications for the future of the Web.

Even if the caps are far above the average users’ consumption, their mere existence could cause users to reduce their time online. Just ask people who carefully monitor their monthly allotments of cellphone minutes and text messages.

“As soon as you put serious uncertainty as to cost on the table, people’s feeling of freedom to predict cost dries up and so does innovation and trying new applications,” Vint Cerf, the chief Internet evangelist for Google who is often called the “father of the Internet.”