In-flight Wi-Fi will eventually take off for passengers aboard some US airlines, but it won't happen before months of testing and slow rollouts of the wireless service.

American Airlines will have one of the largest deployments, with a formal test expected to start "in the coming weeks," a spokeswoman said. The test will be performed on 15 jets and will run for as long as six months. Southwest Airlines, Alaska Airlines, Virgin America and Jet Blue also have limited tests or projects underway.

Some airlines have already announced that pricing will be roughly in line with what it might cost to connect to a Wi-Fi network in an airport for a day -- about US$10 to $12. American has stated that its wireless service will cost US$12.95 for flights that are three hours or longer.

None of the US carriers investing in Wi-Fi expects to offer voice service. They cite federal regulations prohibiting phone calls during flights -- not to mention negative public opinion about the idea of fellow passengers talking on the phone aboard planes. However, some analysts say that if data services for e-mail, instant messaging and Web browsing are a big hit, then carriers might want to add voice service as well.

A big unknown is the performance of the technology itself, including the connection speeds a user will get on a Wi-Fi-capable laptop or handheld device. That's because early test results aren't being made public. However, the airlines say the performance a user sees will be on par with Wi-Fi access inside a coffee shop.

The Wi-Fi signal carried throughout a plane will connect to the Internet via either satellites or antennas on the ground. Some analysts say a satellite connection, such as that offered by Row 44, will provide the greatest coverage. However, American said it has seen success using a ground-to-air system connected to 92 cellular antennas erected nationwide by Aircell.

Adding in-flight Wi-Fi could be an important distinguishing service in today's airline industry, as carriers cut back on amenities and charge for extra baggage as they struggle with soaring fuel costs, several analysts noted.

"Airlines are doing what they can to steal customers, " said Robert McAdoo, a financial analyst at Avondale Partners, who tracks 19 airlines. "But the airlines have to be realistic as to how many customers will pay for Wi-Fi. There will clearly be some users ... [but] there's a question of whether Wi-Fi is going to be big on planes or not."

Here's a rundown on the status of Wi-Fi at several carriers, based on recent interviews and statements:

American Airlines

American ran a free "dress rehearsal" of Wi-Fi service on June 24 aboard a Boeing 767-200 during a regularly scheduled round trip between New York's JFK International Airport and Los Angeles International Airport.

American and Aircell both said they were studying the results of the test and refused to give details, although an Aircell spokeswoman said "customers were excited" about the service.