It's amazing how United makes it sound so positive by stating, "
United's entire p.s.® fleet is now Wi-Fi enabled."
United's p.s. fleet represents just a tiny fraction of United's entire fleet. United is trailing the industry when it comes to Wi-Fi. They seem to be taking a wait-and-see attitude.
The major Wi-Fi provider for domestic airlines is Aircell, doing business as GoGo Inflight Internet:
http://www.gogoinflight.com/
AirTran Airways and Virgin America have Wi-Fi on rolled out to their entire fleets. Delta Air Lines has Wi-Fi on their entire mainline fleet, but not in their regional jets. Other airlines are at various stages. For the status of airlines by aircraft type, see
http://www.gogoinflight.com/gogo/cms/airlines.do
Southwest is using a different Wi-Fi provider, Row 44:
http://www.row44.com/
Southwest Airlines is supposed to have Wi-Fi installed fleetwide some time in 2013.