"We participated in a three-way videoconference call at 50 miles an hour. It was pretty incredible talking to people in the car behind you and to people in an office," Roberts said in an interview yesterday.

He also watched streaming video and saw data coming in live at remarkable speed. "It's like HDTV. Until you see it, it is hard to describe," Roberts said.

After that bus ride, he and others went to work on a $3.2 billion deal, signed in New York at 4:30 a.m. yesterday. In that transaction, Comcast Corp. joined with other cable companies, a chip-maker, and two wireless-phone companies to create a new venture it says will provide high-speed Internet-on-the-go in the nation's top 100 markets by 2010.

The new technology, called WiMAX, will transmit high-speed Internet, movies, television shows, sports games, and other digital data from about 200,000 existing cellular-telephone towers to laptop computers, telephones and other devices.

The deal creates a new company called Clearwire Inc. Its owners will be Comcast, Sprint Nextel Corp., Intel Corp., Google Inc., Time Warner Cable Inc. and Bright House Networks L.L.C.

They have agreed to collectively invest $3.2 billion. Comcast's share is $1.05 billion.

The deal is expected to close by the end of the year.

"We'll be on the offensive in wireless with world-class partners. It is exciting. Our customers will know that the Comcast experience will be not just in your home but wherever you want it," Roberts said.

The new company is organized to avoid cumbersome decision-making among the big corporate owners about what to do next.

Sprint and Clearwire will build and operate the system. Intel will make the chips that allow computers, cell phones and other devices to receive the signal. Google and the cable companies will rent time on the network to distribute their products and services.

"Comcast will be in control of its own destiny, offer its own services and brands. Google will do its thing. Intel will sell chips," Roberts said.

Comcast and the other owners will have access to Sprint's existing slower third-generation, or 3G, wireless network in areas where the new 4G service is not yet available, Comcast said.

To get a head start on the next generation of wireless, Comcast and the others are betting on technology not yet tested on such a grand scale.

Comcast insists that it has done a lot of research on the technology, which is already in use in Australia and parts of Asia.

Comcast's role began late last year, when its new chief financial officer, Michael Angelakis, along with senior vice presidents Robert Pick and Tom Nagel, saw a WiMAX demonstration at a technology show in Las Vegas.

A short time later, Roberts and his chief operating officer, Stephen B. Burke, flew to Portland to meet with cell-phone pioneer Craig McCaw, who will be chairman of the new Clearwire company, and to go on the demonstration bus ride.

"We invited Google to go with us, and they sent someone," Roberts said.

After that bus ride, Roberts said, he agreed to line up other cable companies and work on the deal signed yesterday.