There has been pressure from US authorities to add some sort
of remote deactivation function to handsets, although there have also been
concerns about how to make such a feature strong enough to make it irreversible
by a thief, yet not too easy to use maliciously
A kill switch would let an owner remotely disable the handset
in such a way as to render it essentially useless. However, as that action
shouldn't be reversible, it has to be designed to be secure from being triggered
by hackers.