ATLANTA — Delta Air Lines Inc. said Tuesday it will offer broadband wireless Internet access on its entire domestic mainline fleet by the middle of next year.

The Atlanta-based company said Wi-Fi service will be offered for a fee to customers traveling throughout the continental U.S.

The nation's No. 3 carrier is partnering with Aircell, an airborne communications provider, to install the network on Delta's domestic fleet of more than 330 aircraft.

The system will allow Delta customers traveling with Wi-Fi enabled devices — such as laptops, smartphones and PDAs — to access the Internet while in flight.

A flat fee of $9.95 will be charged on flights of three hours or less, and $12.95 on flights of more than three hours.

The service will be offered initially on Delta's fleet of 133 MD88/90 aircraft and will expand to the remaining domestic fleet of more than 200 Boeing 737, 757 and 767-300 aircraft during the first half of 2009. It expects to have the technology installed on its entire domestic fleet by next summer.

Financial terms of Delta's agreement with Aircell were not released. The airline did not say how much it expects to generate in revenue by offering the service on its mainline domestic flights. It also did not say in a statement what its plans are, if any, for offering Wi-Fi service on international flights.