A Cheese Box (named for the type of box the first one was found in) is a type of box which will, in effect, make your telephone a pay-phone.
These were first used by bookies years ago as a way of making calls to people without being called by the cops or having their numbers traced or tapped. They would place the cheese box in an empty appartment connected to two lines. If the cops traced their call they would only find an empty appartment.