The current wisdom boils down to 'not with an engine running'- and this is what will be enforced.
Some pilots have been known to experiment with mobile phone useage. It would appear that once airborne and the signal being received by several ground stations, the phone is 'sent to Coventry'. Why this should be I have no idea- maybe to protect the network from being flooded with signals from the same phone. Down on Terra Firma, the network re-appears.