You may also find that if you used your spiv phone in flight, you would breach the contract with your provider and they would terminate your contract.
Has this ever happened?
The network provider cannot tell - other than through analysis of base station connections and even then airborne use will be inconclusive because there will be no altitude data.
Countless airline passengers embark with their phones ON and these phones continue to connect to base stations for the first few thousand feet up. If people were getting cut off, we'd know about it by now.