Avoid returning unknown international numbers

Recently a problem for telecommunication operators was created called "Wangiri Scam" or "Wangiri Fraud" that attackers provide premium rate numbers (are numbers for telephone calls during which certain services are provided, and for which prices higher than normal) and randomly call to phone number in all over the world and immediately disconnecting in the hope those who are targeted will call back, Once they do return the missed call they will be re-routed to premium rate number and charged a lot .It encourage costumers to speak longer with subjects such you won a lottery or etc.
Unfortunately there is no way to identify a scam call number, Do not call back any unknown number that leaves you a blank voicemail message or missed calls.
Be ware if customers fell into this problem, they responsible for their charges.