What is the origin of the idiom "drop a dime on someone" and when to use it?

The idiom "drop a dime on someone" originates from a time when payphones, also known as public telephones, were commonly used for making calls. In the past, it cost ten cents (a dime) to make a local call from a payphone. Therefore, "dropping a dime" on someone referred to making an anonymous or discreet call to report a person's illegal or suspicious activities to the authorities or someone in a position of power. This idiom is used to describe the act of providing information, typically to the authorities, that exposes or incriminates someone's wrongdoing. It implies that the information is shared secretly or anonymously, often as a way to avoid personal involvement or consequences.