Though this might not be as useful now because most of use smartphones. For the sake of those who make need it, I'll do a tutorial on how to solve it.

I first encounter this last October 2014 when an old folk brought to me his phone with that issue.

In some cases like changing your SIM Card, your phone might not read the new SIM card or any other cards beside the one you originally used and showing the error "Illegal use will be powered off soon" then shutdown. 

Your problem cannot be solved unless you factory reset your mobile phone. The problem is that when you go to Setting and try to Factory Reset it, it requires you to enter the default password.

Okay, the password you needed is simply 4-digit zero (0000). I already tried it and it works.

Thank you and stay tuned for more geeky tuts..