Switch them off
A possible solution to on-board mobile phone use at inopportune times is to install one or more universal microcell transmitter/receivers. The basic technology would be that proposed for authorised in-flight mobile phone access, where the radiated power is high enough to capture any phone on the aircraft that happens to be switched on, but low enogh to avoid interferene with the aircraft electronics.
Such a system could cut off all communication between on-board phones and the outside world. It could go further and discover any phones that happened to be switched on but not in use. With two cells, it would probably be possible to locate such phones to the seat row, but probably not to an individual seat. Further refinements could include calling all switched-on phones that are inactive with a demand that they be switched off.
This should be a patentable invention. If anyone has already patented it, then I apologise to the rest of the world for possibly leading them into a violation of patent rights. If it is not already patented, then its too late for anyone to make a valid claim. The idea is now in the public domain.