Krista Dietrich relishes the rare opportunity to sit back in her airline seat and shut off her mobile phone. But the simpler days of reading or napping on planes are soon to be replaced by Web surfing and instant messaging.

Delta Air Lines announced Tuesday that it will introduce Wi-Fi access on certain aircraft by fall and expand it to its entire domestic fleet of more than 330 planes by next summer. American Airlines and Virgin America previously have said they will launch in-flight broadband Internet services on certain planes by year-end.

Efforts to turn planes into Wi-Fi hot spots are expected to generate a fresh source of revenue for airlines and begin to alter onboard culture. Planes were among the last places where people could be unreachable. Increasingly, however, passengers clamored to use their BlackBerries and laptops while in the air.

Atlanta-based Delta's service, dubbed Gogo, will cost $9.95 for flights of three hours or less and $12.95 for flights over three hours.

"With the Delta announcement, you really hit the tipping point," said Jack Blumenstein, chief executive of Itasca-based Aircell LLC, which makes the system for Delta, American and Virgin. "Frankly, every other airline has to join in."

JetBlue Airways has limited connectivity on a single aircraft dubbed BetaBlue, while Southwest Airlines and Alaska Airlines are conducting their own tests. United Airlines spokeswoman Robin Urbanski said the Chicago-based company is looking into different Wi-Fi technology providers but hasn't announced a launch.

Airplane broadband speeds will be a touch slower than high-speed residential service, said Henry Harteveldt, an analyst at Forrester Research. This means passengers can send e-mails and browse most Web sites, "but you do not want to get on the plane and decide that's where you're going to download the digital version of 'Gone With the Wind,' " he said.

JetBlue's service is free but doesn't allow full Internet access. Passengers can browse Amazon.com and check e-mail from major sites such as Yahoo, Hotmail and Gmail.

But even as Wi-Fi spreads, don't expect mobile phone service anytime soon. Carriers say customers balk at the idea of being trapped next to a gabby seatmate. Many airlines also are blocking applications that enable calling over the Internet, such as Skype. They say instant messaging and texting allow good communication without the disruption of a voice call.

Mobile phones should stay turned off during flights, for now. A bill to ban the use of cell phones on commercial flights passed a House of Representatives committee vote last week and will head to the full House for consideration.

"I feel pretty strongly about people not using their mobile phones on planes because you know what it's like even on the train," said Jonathan Goldman, a commercial real estate broker in Chicago. He said he would pay for in-flight Internet access if rates were reasonable.

"There's nothing wrong with getting more work done on a flight," said Goldman, 43. "Boston to California or Chicago to London - that's a huge amount of time where you could be really productive. Just learn how to shut down for dinner or for an hour."

Brad Newberg, 36, a Washington, D.C., lawyer departing from O'Hare International Airport on Tuesday afternoon after a business trip to Chicago and who flies 30 times a year for work, said he might even pick his carrier based on its Wi-Fi offering.