Whether they are from banks or scammers ill never give information via phone, even from mobile company asking for information for upgrade, even if they are legit i will never give up info over the phone, unless I'm the one who call them via their official telephone line, what i always do is go to the bank if i have trouble, or if my postpaid have issues, and that can't be resolve via phone, you can't trust this people that are calling via phone, who knows if its been hack or something.
It is not wise to give someone you know your information to, especially those that call from a mobile phone; they are true scammers. If not, how will a person approach someone he does not know and warn him or her that his or her bank is experiencing problems by requesting their information?
And, because some people are unfamiliar with the bank system, they will be hesitant to provide them with their information. That is how some people are easily scammed; instead of going to their banks and complaining to customer service, they wait until after they have been deceived by scammers, and they will later regret it.