Verizon tested out an air-to-ground system to the FAA's satisfaction says the Wall Street Journal: But the frequencies in question aren't cleared for broadband use and are up for auction for that purpose. The auction might happen this fall. United has to clear each model of plane they fly to demonstrate that the Wi-Fi and air-to-ground systems don't cause aeronautical system interference, although it's pretty clear that Wi-Fi isn't an issue given how many laptops must already accidentally have Wi-Fi signals shooting around on planes.
Speeds in use aren't discussed, but the amount of bandwidth up for auction is a total of 8 MHz which might be divided into a 2 MHz and 6 MHz band or two 4 MHz bands. You can't take a 1:1 relationship from MHz to Mbps, but it typically hasn't been far different. Wi-Fi has a 20 MHz stretch that delivers net throughput of about 20 Mbps; 1xEvDO uses 1.25 MHz for a peak download speed of about 1 Mbps, with 200 to 300 Kbps more typical.
United hasn't released pricing yet, but plans to have service on all North American flights by late 2006. A Verizon competitor, AirCell, already operates an extensive network of ground stations for business flights and expects to have a similar system it can offer to airlines that it would charge $10 a flight for.
The New York Times has a story with a little less and more than the Journal's coverage.