Just charge £5/minute for using the on-board link. That'll discourage people, at least after they've done it once and get the bill. Then it'll only be the suits in business class who don't have to pay for it anyway, but at least cattle class at the back will be OK.
As for final approach, the solution is possibly not to turn off the pico cell but turn off the satellite link. That'll keep all the phones at minimum power and locked to the picocell instead of trying to contact something outside at full power. It'll also keep the interference to short bursts rather than a continuous signal.