NEW YORK - A new era in Internet access was set to take off yesterday as a JetBlue Airways flight from New York to San Francisco offered passengers limited e-mail and instant messaging in the air.

The milestone commercial flight, a first for a U.S. airline, heralds a coming trend of Wi-Fi in the sky as U.S. carriers including American Airlines and Virgin America prepare for 2008 rollouts of even more robust Web services.

"People want full Internet access from the sky," said Forrester Research analyst Henry Harteveldt. "Within the next 12 to 24 months, U.S. airlines that don't offer in-flight Internet access - at least on medium- and long-haul flights - are basically telling business and frequent travelers: 'We don't want your business.' "

Having a low-cost carrier pioneer the technology proves that it is practical and desired by young travelers, he said. Harteveldt flew on JetBlue's Internet-equipped plane during a test last week and planned to fly during the public debut yesterday.

On that trip, JetBlue Flight 641 will be a plane dubbed "BetaBlue," an Airbus A320 used to test entertainment services from JetBlue's LiveTV subsidiary.

On board, the carrier will offer free wireless access for passengers with laptops or handheld devices through Yahoo mail and messaging software.

Two BlackBerry models with Wi-Fi (the 8820 and 8320) will also allow access to corporate e-mail through a partnership with BlackBerry maker Research In Motion.

Passengers with those devices will still have to turn off their cellular transmitters during flights. All electronics also must remain off during takeoff and landing.

Passengers also won't be surfing the Web or sending e-mail attachments because of bandwidth limits.

The JetBlue service provides access above the continental United States by communicating from the air with about 100 radio towers.

LiveTV purchased access to wireless airwaves once used for airline seat-back phones so they do not interfere with cellular service on the ground.

Virgin America and AMR Corp.'s American Airlines are embracing a similar air-to-ground approach using technology from Aircell LLC, which has locations in Colorado and Illinois.

Those services, with fees akin to ground-based Wi-Fi hot spots, should offer a fuller Internet experience with Web surfing and speeds similar to a phone company digital subscriber line (DSL) connection.

Virgin America also plans to integrate the Internet into its seat-back entertainment system, providing access for passengers without laptops or Wi-Fi gadgets.

Alaska Airlines plans to test an in-flight broadband system in the spring that connects planes to satellites, providing more coverage than land-based towers. The technology from California-based Row 44 is intended to work across North America, above Hawaii and during over-water flights.

Several international airlines once offered Internet access through a Boeing Co. satellite-based service called Connexion, but the aircraft maker ended the service last year after failing to find enough customers. A big factor was the Sept. 11, 2001, terror attacks, which left U.S. airlines struggling for financial survival.

For JetBlue's Wi-Fi flights, Yahoo created special lightweight versions of its software to work smoothly in the air, said Brad Garlinghouse, Yahoo's senior vice president of communications and communities.

JetBlue's test flight last week was good but not perfect, Harteveldt said. He said there was one 20-minute wait while the system restarted.

Customer comments from initial flights will help shape how JetBlue adds more features and spreads the service to all its planes, JetBlue spokeswoman Alison Eshelman said.

JetBlue is willing to explore silent options for communications services, but not cell phones, since customers oppose phone chatter in the air, Eshelman said.

With that in mind, the ability of the BlackBerries with Wi-Fi to make Internet-based phone calls will be blocked on the BetaBlue flights, she said.

Social pressure from unhappy passengers will also likely keep potential Internet callers from jabbering away, Harteveldt said.

"It's not like you can run and hide on an airplane," he said. *