To take WiFi out of the home and provide Internet access to strangers involves a few changes. Sometimes, the WiFi antenna has to be moved to rooftops to allow the signal to go farther, with other antennas on nearby buildings to relay it.

Companies that charge for service, and therefore don't want freeloaders riding their airwaves, also have to deploy software to control access by subscribers. For-pay WiFi services may also provide extra security with "virtual private network" software that encrypts network traffic.

Many companies think they can make a profit from this -- even while some of them have already gone bust in the attempt. The best-known WiFi businesses consist of networks in cafes, hotels and airports that are marketed to business travelers and Internet addicts who might subscribe to a second Internet access service to get that connectivity away from home. Some are start-ups (Boingo Wireless, Cometa Networks, Wayport and Wise Technologies, to name a few), while others, such the wireless-phone firm T-Mobile USA, market WiFi as an adjunct to existing services.

Wayport has installed WiFi in 30 Washington area hotels and saw traffic double in Washington and around the country last year, said Daniel Lowden, vice president of marketing for the Austin-based company. An average of 9.8 percent of people staying in those hotels use their wireless service -- lower than the 25 percent usage rate in the San Francisco area but above the national average of 6 percent, he said.

Wayport now has 170,000 daily or monthly subscribers, up from 50,000 a year ago, Lowden said, and will generate enough cash to cover operating expenses within a few months. Prices range from $6.95 for one-time usage within an airport, to $49.95 monthly unlimited service at any Wayport access point.

Wise Technologies is making its own attempt to blanket the Washington area with WiFi; so far it has 50 hot spots deployed in places from Baltimore-Washington International Airport to the Zanzibar nightclub in Southwest, said Gary S. Murray II, president of the privately held Landover firm. Wise was founded in 2001; it has more than 2,200 users and is growing by 10 percent a month, he said.

For the moment, Wise isn't interested in expanding beyond Washington -- its target is to double its number of hot spots by the end of the year, Murray said.

A separate set of firms, mostly smaller local companies, are using WiFi to transmit high-speed Internet connections to areas that lack alternatives to slow, dial-up modem access.

Laurie Dunham founded East Statford Wireless Internet Service LLC out of her Leesburg home last July, when neither cable-modem nor digital-subscriber-line service was available in her subdivision.

"Let's take the bull by the horns," she said. After sending leaflets to neighbors, she and her engineer husband, Rich, discovered they had enough nearby interest to set up their own Internet service. They set up specialized antennas on rooftops and now provide access at $45 a month to 30 neighbors who live within a one-mile radius of their home.