I have seen too that episode of the Mythbusters but I think they tested on a rather basic aircraft.
Normally, the more systems an aircraft has and the more complex these are, the probablility increases that radio waves "find" some metal loop somewhere to trigger an electric impulse.
Moreover, the more an aircraft depends on electronics (like in "fly by wire"), the more vulnerable it is for such a parasite electric impulse.
By the other hand, the overall probability of such a mishap is certainly low, otherwise cellphones would be simply banned (like so many other objects in these days). Could you imagine a hijacker go to the cockpit with his cellphone and anounce "Divert to NOW ... or I call my mom" ?
And still, while travelling myself, when i see people who distregard the cellphone announcement, the thought that THEY take even 0.000....1% chances to hve ME torn to pieces because of THEIR calls does not feel good. So I won't blame those italian pilots for taking action.
Andrei