Being online while being airborne is fast becoming reality for U.S travelers. American Airlines (AMR) is announcing on Tuesday that it’s joining rival Delta Air Lines (DAL) in making Wi-Fi Internet connections available to most domestic passengers.

American, No. 2 in the world in passenger traffic after Delta acquired Northwest Airlines last year, says it will equip more than 300 planes used primarily in the U.S. with high-speed Wi-Fi capability. Delta said in December that it would offer the service on its planes by the end of this year and on newly acquired Northwest planes by the end of next year.

Virgin America expects to have its fleet of 28 planes outfitted for Wi-Fi by the end of June. American’s announcement accelerates what largely has been a limited service offered by revenue-starved airlines to see whether passengers would pay for the access. It follows a six-month trial that Dan Garton, American’s executive vice president of marketing, said gave customers "the chance to choose to remain connected to work, home or elsewhere when flying," and the airline a chance to study "customers’ willingness to take advantage" of it.

Southwest Airlines (LUV) and JetBlue (JBLU) also are experimenting with it on planes flying in the USA. American’s service will cost laptop users $12.95 on flights longer than three hours, and $9.95 on shorter ones. Travelers using handheld devices, such as smartphones and PDAs, will pay $7.95 no matter the length of the flight. The service will be available only after planes reach 10,000 feet so it doesn’t interfere with communications between the cockpit and air traffic control.

International flights aren’t being equipped with American’s Gogo in-flight Wi-Fi system developed by Aircell because it operates on ground-to-air signals from cellular towers. Southwest is experimenting with a satellite-based system that would allow access on international flights, though it flies only domestic routes. Despite the airlines’ push to keep customers connected while flying, there’s one service passengers shouldn’t expect soon: cellphone service.

Carriers are reluctant to make cellphone connections available during flights, partly for technical and bandwidth reasons and partly to avoid problems between passengers seeking quiet and those talking loudly to be heard above flight noise.