" Apologies for yet another bonehead question from the SLF.
We are continually told to turn off mobile phones and laptops on landing as these can effect the aircraft systems. "
More to the point, it affects the profitability of existing in-flight telephones.
The idea that cellphones interfere with the avionics is
AFAIK totally unproven. However it's never been totally proven that they couldn't either.
However plans to introduce 'approved' systems for inflight cellphone use suggest that it's largely not a real concern.