But the big potential problem I see with inflight cellular is not outbound calls/SMS/VoIP - it's the inbound traffic & associated ringtones.
2-hour shorthaul flights are pretty noisy anyway, as they're in daytime, with announcements and catering trolleys and kids going on holiday. And I'd certainly imagine that few people would be so socially-unaware as to initiate noisy conversations during the hours of "darkness" on a longhaul flight. But the issue has to be sleeping in a cabin with 200 other people who could well be *receiving* SMS or calls from people (or computers) in their home timezone, unaware they're midflight.
If you work out the stats it starts to be quite scary - on a full 747 you can have about 100 people within earshot, say 10 rows around you - so I'd guess that during a 5-hour "lights off" part of an overnight flight, you could easily get 30+ inbound events with associated ringtones.
One option might be to make the inflight system accept outbound traffic only, during "dark" hours. Or just instigate a rule that all phones/PCs have to be used with headphones only, and that any ringtone offenders get moved to a spare "sin bin" seat next to the lavatories.