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 seemingly 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 exemplar 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.
(1) I am mainly interested in technical explanations of the phenomena, i.e. whether it is indeed true, and if yes how, that the SIM card in my mobile phone got manipulated, and personally deem it neither favorable, nor essential, realistic, etc. to conjecture on the motivations behind such manipulations, if these indeed happened.
(2) Googling with e.g. "cell phones calling themselves" will turn up a lot of apparently similar cases which, I guess, could stem from diverse different causes in practice. It seems that there have not been much scientifically exact and detailed investigations done on the issue and that the phenomenon can occur both to modern smartphones with Internet access (hence higher liability of being hacked) and to the non-smart mobile phones without Internet access.
M. K. Shen