For call-in talk shows, screeners determine the air quality of the call (good connection or not) and if the caller's comments will further the topic or add a new point.
Richard Roeper blamed call screeners in 2003 for a phone prankster getting through to Dan Rather live on-air during the Space Shuttle Columbia disaster, by not checking the area code of the caller, who claimed to be an eyewitness in Texas.
[4][5] A New York Post article about phone pranksters describes call screeners as "overburdened and generally young producers assigned to act as gate-keepers", whose tools include "simply to ask would-be callers for their phone number and make sure the area code matches up with where they say they're calling from."
Other techniques described "include grilling the caller on little known facts about the situation or organization they claim to represent.
Many live call-in radio shows do not like alternative or adverse opinions to be aired, going through great lengths to screen out such calls.