The days of endless web surfing for an absolute, controlled fee each month may soon be over. Three of the U.S.’ mammoth Internet services could begin putting monthly limits on the online activity of their most assiduous users, CNBC reported Sunday. Times Warner Cable, AT&T and Comcast have admitted they don’t see it as fair to charge the same amount for folks using the Internet simply to check email as for those spending hours online each day, downloading large music and video files. So the three have cooked up different ways they could deal with the broadband use imbalance.

Times Warner Cable set off a trial “Internet metering” in Beaumont, Tex. earlier this month (we covered here). The trial offered customers a choice of monthly plans, one with a 5 GB cap, another with a 20 GB cap and the last with a 40 GB cap, each costing within a $30-$50 range. The company would require users to pay an additional $1 for each GB surpassing the bandwidth limit. AT&T considered similar measures.

It explained that somehow limiting extensive use was unavoidable for a service hoping to stay afloat. So, AT&T said, pricing-by-data-volume was merely a logical next step.

On Thursday, Comcast told The New York Times it would likely keep Internet traffic to manageable amounts during peak times by having connections for “bandwidth hogs” stay slower than for those of less enthusiastic users.

While 95 percent of customers use fewer than 40 GB per month, the remaining 5 percent use over 50 percent of the network’s capacity streaming video on Hulu, purchasing high-quality material from iTunes or even working with such services as Vonage and Skype.

“Father of the Internet” and Google chief Internet evangelist Vint Cerf said that such charges could cause people to accommodate their usage that it fall within the limits, writing in an email that “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 [the] trying [of[ new applications.”

But tech company Cisco put in a report that “today’s ‘bandwidth hog’ is tomorrow’s average user.”

Whatever usage patterns become, the honeymoon period of rent-controlled hours-long web searches are likely numbered. Perhaps there really is no such thing as a free lunch (or Internet).