The wi-fi that is available on US domestic carriers (eg Virgin America) is cost effective because they are using base stations on the ground under where they are flying. One of the reasons Connexion was killed was that the satellite costs were too high. So most international carriers who do their flying over water won't be able to utilise the technology used by US domestic carriers.
I believe the base stations are separate to the GSM signal and specially setup for GoGo. But I might be wrong about that.
I've actually done a lot of Satellite Internet (used to work for one of the companies that pioneered it in Australia for large-scale pipes, 45mb and above back when ISDN was considered fast).
Satellite itself isn't so expensive. It's the fact they need to have something that can actually keep a lock on the bird itself, and the fact that it's a high-latency item (even at 10km up in the air, you've got to bounce the signal up to around 35,000km for a Geosync bird). It typically adds around 300-350msec to a packet of data, making it pretty unusable for any real-time applications (even though most carriers are keen to prevent VoIP stuff as it may bite into any small revenue they have from the in-seat phones).
Transponder space/pricing isn't that bad but getting the coverage is. There's a reason there's so many birds in the sky and that's cause they only have limited footprints. It's easy enough to hand off to another transponder on another bird, but the actual cost of the tech on-board made it prohibitive at the time. Sat pricing is a lot better now.
I'll save the technicalities of other issues with sat for later
