(FORTUNE Magazine) – Not so long ago there was handwringing among technology gurus about the unexpectedly slow rollout of broadband. With the recent rush to install wireless Internet access, popularly known as Wi-Fi, in what seems like every coffee shop and airport, that worry has largely gone away. But I'd like to suggest that no one--not even today's Wi-Fi evangelists--is mentally prepared for a world in which high-speed Internet isn't just easy to find but pervasive. That world is going to bring all sorts of grief to telcos and all kinds of benefits to consumers and business users. Which is why now is the time to think about what life will be like in a world in which broadband access is cheap and ubiquitous--I call it CANDU.

First, the state of things today: People can get Wi-Fi access now--for a price--while nursing a latte at Starbucks. Increasingly, Wi-Fi is also appearing at trade shows, offices, and anywhere else workers may be stationary for more than 15 minutes. The cities of Paris and Adelaide, Australia, have committed to providing complete urban Wi-Fi, New York City is seeding its parks with free service, and Verizon is converting all its New York City pay phones into Wi-Fi transmitters.

The speed of the service is quickly improving too. Wi-Fi's standard 802.11b version allows for sending and receiving files at speeds of up to 11 million bits per second. That's fast enough to allow you to watch seven streaming movies simultaneously. (Web surfing via Wi-Fi, however, is often much slower because of the limitations of the home or office Internet pipes to which the service connects.) In Wi-Fi's new 802.11g version, the transmission rate gets juiced up to about 54 Mbps--all using equipment that sells for just a few hundred dollars. And these are just the early days.

Ken Arneson, CEO of Chameleon Technology, thinks Wi-Fi will get much faster still. His company has commercialized defense-related communications technology and overlaid it on Wi-Fi, offering a solution to Wi-Fi's problems with security, tolls, and switching. Arneson's best guess on Wi-Fi capacity in five years: 500 Mbps to 1 Gbps. Other telecom execs I know are guessing as high as 10 Gbps. The speeds will encourage people to develop high-bandwidth habits--say, beaming live TV signals of various channels to different digital TVs around the home while retrieving video or audio and sending it elsewhere. High speeds will also allow greater numbers of users, both machine and human, to interact simultaneously.

But what use is all that speed if you have to be sitting next to a Wi-Fi transmitter? Today Wi-Fi can be broadcast only about 300 feet from a base station. Future units may easily extend that to 1 1/2 to three miles, allowing more coverage in more areas. How will they do that without interference? People like Craig Mundie, Microsoft's chief technical officer, think that the devices may become smart enough to sort out signals and noise, perhaps aided by a band of spectrum set aside purely to handle traffic control; experts on the cellular side aren't so sure.

Now imagine the new CANDU landscape. In cities broadband will be everywhere, with enough capacity to handle all users. In semi-urban and less dense environments, Tinker Toy--like networks built from focused beams--which in recent experiments have been able to travel 15 to 30 miles--along with central dispersion points and line-of-sight home antennas, will create extremely high-bandwidth access almost overnight.

The cost of CANDU broadband: In dense areas it approaches being free. In rural areas homeowners might have to pay a few hundred dollars in equipment costs. Operating charges will vary greatly, depending on whether private companies or public utilities (a growing model) are selling the service.

Once broadband is ubiquitous and cheap, consider what happens to telephony. You would never know it, but about 30% of U.S. long-distance calls already travel not on conventional phone networks but on the Internet. CANDU broadband should steal even more traffic from the big telcos. Cisco, the company that most looks like the future telecom equipment supplier (and in which I own stock), began shipping its branded Wi-Fi phone last month. It allows voice calls to be carried over any Wi-Fi network anywhere. We'll see major handset vendors, including Motorola, shipping Wi-Fi phones by year-end. Critics carp that there is no way to roam between Wi-Fi networks; that, too, will get worked out over the next five years.

The result: If you use a Wi-Fi phone at a free broadband access point, you can call France and talk forever, for free. You can turn on your Wi-Fi laptop and download whole movies from the public domain, for free. You can set up a visual conference, swap files, or even create a mesh or grid computing system with your peers, building the largest supercomputer in history, for free.

It's the CANDU spirit at work.