The Gogo network may be cellular, but their network is designed to hit a target flying 500 miles per hour at 39,000 feet. Plus, the base station on the aircraft concentrates the traffic, which means there's one air-to-ground link per plane, rather than per handset as would be the case of someone using an unauthorized cell phone inflight today.
It's also not true that all the existing inflight data links are cellular. Southwest uses Row 44, which provides a satellite based solution. JetBlue is planning to launch, if it hasn't already, a satellite-based system with ViaSat.
There are other, older, slower options for inflight data access that are satellite based, but we're talking about dialup speeds here.