Delta Air Lines said in August it would deploy the Aircell system on all the planes in its main fleet by summer 2009, which in the U.S. ends at about the end of August. American Airlines is offering a service on a limited-time trial, as is JetBlue.

The demand is there from passengers, especially business travelers, but whether more airlines commit to permanent commercial services will depend on price and performance, two longtime wireless analysts said on Thursday.

Key unanswered questions include how well the technical controls will work if someone tries to make VoIP calls or hog the Internet connection with movie downloads, and how the airlines will solve passengers' technical issues without an onboard IT staff, said Jack Gold, principal analyst at J. Gold Associates.

"Users are going to have problems. It just happens," Gold said.

Any new source of revenue will be attractive to the cash-strapped airlines, said Gartner analyst Ken Dulaney. The economics of in-flight broadband have improved since the days of Connexion, with lighter on-board systems helping airlines meet tight budgets for weight, he said. But as a discount airline, Virgin may have a harder time than some at selling the service, Dulaney said.