American Airlines offers in-flight Internet access.

In partnership with Aircell a telecommunication company, American Airlines has started since August to offer in-flight Internet access on Boeing 767 aircraft's from New-York to Los Angeles, San Francisco and Miami. The service is named Gogo and is a six months trial program. According to the New York Times, with the service, you can send emails, instant-messages or surf the Web. One thing you can not do with it, is connect to VoIP services like the one offered by Skype, to make phone calls via the Internet. Gogo technology is capable of allowing it but a filter have been put in place to prohibit it. Another restriction that has been just added, is the ability to visit adult sites.
For a cross country flight, the gogo service costs $12.95.
Delta and Virgin America are in the work to offer the service by year end while Air Canada plans to do so by next spring.

For more see NY Times