said by TKJunkMail :

They are using EVDO technology, but from looking at the Aircell web site, IT APPEARS like they have their own towers and assigned private frequencies from the FCC. So they won't be sharing service with Sprint, Verizon, etc. Also the shared bandwidth for the plane should be higher than the typical EVDO bandwidth available to a Sprint or Verizon cellphone user. But it will still be shared bandwidth for however many people use the service at one time on the plane, and however many planes may be leeching off 1 tower at the same time.

Since you are going thru the aircell gateway, I suspect they will be able to block any protocols they don't want being used. So using VOIP may be very diificult if they really want to block it.