The budget European airline will eventually equip all plans with OnAir service: They'll start with 50 planes by the end of 2007, and expand to what is now a 200-plane fleet. OnAir has told me in the past that they don't have total control of the end price--that will be set by mobile operators that allow the roaming--but prices will be in line with international roaming, so at least $2.50 a minute. Ryanair isn't mentioning pricing yet. I expect that text messaging and other text-based services, such as Blackberry email, will represent a significant portion of use for social and cost reasons.
OnAir backhauls its service over Inmarsat satellites, and it's waiting for regulatory (FCC analogs) and airworthiness (FAA analogs) approval for its approach. They expect to launch Air France in the first half of 2007, followed by regional airlines in Portugal, the British Midlands, and now Ryanair.
Qantas, by contrast, will try out Aeromobile's service, which relies on slightly older Inmarsat equipment at the moment. Qantas will run a test of the service for three months on a single Boeing 767 on domestic routes in Australia.