how will Ryanair cabin crew distinguish between those who are legitimately using their system and the morons who are trying to get a signal on their own networks?
They won't need to.
The local base station in the aircraft can be designed to block access to outside networks by mobile phones within its range (i.e. inside the aircraft).
As an additional benefit, it will be able to block outside access whilst withholding access to the on-board system. Thus all mobile phone use can be blocked during takeoff and landing phases.