[Cryptography] Bizarre behavior of a non-smart mobile phone

[mok-kong shen]

That a modern smartphone with Internet access and a multitude of nice 
features is liable of being hacked
similar to a PC is evident. On the other hand, a non-smart mobile phone, 
of design of the earlier
generation, unintelligent, clumsy, no Internet access, though yet 
purchasable for telephone and SMS
purposes only, could IMHO easily mislead one to think that the device 
may be sufficiently secure against
malicious manipulations. The fact, I presume, is however that, if an 
adversary is capable enough to enter
the cellular network, he could access the SIM card to perform his 
malicious work. A recent personal
experience of mine is the following: I bought such a device and a 
pre-paid SIM card, entered the
telephone numbers of my friends into its contact address list and 
informed my friends of my new mobile
phone number. Soon, though at a rather low frequency averaging roughly 
one event per day, a number of my
friends complained that I had called them but strangely never attempted 
to say even a single word. It
turned out that the device each time arbitrarily selected an entry in 
the contact address list and called
automatically, which could also be verified by its list of all outgoing 
calls. As remedy I deleted all
telephone numbers of my friends in it, leaving however for experimental 
purpose my own home telephone
number. One following night I had then the uncommon experience of being 
awoken by a call from my own
mobile phone! (Actually two new mobile phones of the same brand were 
tested. Following my complains of
the said phenomenon, the vender gave me a new examplar in exchange, so 
that the probability of there being
a manufacturing problem is vanishingly small.)

Another phenomenon that co-occurs with the above is that the device 
powers off automatically at a
frequency comparable to the first, even though its battery is 
sufficiently loaded.

Being a layman in such issues, I should be very grateful for exact 
explanations of the phenomena.

M. K. Shen