To eliminate suspicion that bank employees are in collusion with the criminals, banks can consider installing mobile phone jammers and monitoring all landline conversations.

Alternately, bank clients can opt to bring along a handheld jammer when they go to the bank to withdraw cash, since it more likely a bank employee would text his/her criminal partner than make a voice (landline) call for fear of being overheard.

Or course if the criminal happens to be one's own (ex-) employee or a bank outsider, then having a jammer would not help at all.

Note though mobile phone jammers are illegal in several countries. I am just not sure whether it is illegal in the Philippines or not.