There is a relatively new French helicopter in service, that IS affected by mobile telephones. I have been informed by 2 engineers who work on them, that if an outgoing call is made from the pilot/co-pilot seat, (while aircraft is on ground, before start-up) it will cause interference on intercom and radio transmissions.
Why risk it?, would you want to be in the back of a large fixed wing, coming into land on a stormy night, knowing that there is a very slight possibility that the person sitting next to you could cause a problem with the ILS or autopilot, by calling for a taxi.
I know modern aircraft wiring is well shielded, but it doesn't take much for this shielding to break down.
Autopilot and ILS systems operate with tiny inputs in the millivolt range, which I'm sure it's possible for mobile phone to emit.
Mr G