I also have some difficulty with the idea of someone trying to use a mobile in a helicopter at low level in those days.
Kilo52,
I am interested that you do not seem to have similar difficulty with the idea of two highly trained and skilled pilots flying in IMC so close to high ground.
Mobile phones have always caused interference to certain electronics either when they are called, or when they hand over from one station to another, exactly what any phone would have been doing as you cross from NI to Scotland if it was switched on.