Hi,
an extract from Airbus 340 FCOM Bulletins:
A study has been conducted by an RTCA (Radio Technical Comission for Aeronautics) special commitee.
- The conclusion is that the probability of a passenger-operated device interfering with the ILS localizer during a typical flight is about one in a million.
Airbus Industrie recommendations is that no portable device should be used during take-off and landing.
Hope it helped.