I have had the note below come in.
If you receive a phone call on your mobile from any person, saying
that he or she is a company engineer, or telling that they're checking your mobile line, and you have to press #90 or #09 or any other number, end this call immediately without pressing any numbers.
There is a fraud company using a device that once you press #90 or
#09 they can access your "SIM" card and make calls at your expense.
Forward this message to as many colleagues, relatives and friends as you can, to stop it.

Never heard that one, but I know on landlines, if your asked to press 9 by someone, don't as it can initiate reverse call if you call them, or if you phone them on a cheap number, it allows the call rate to be increased. I can't remember which one though