Well, looky here! From the Columbia Journalism Review:
Well, here’s a shocker: Some of the people who phone in to talk radio shows (that caller with the pitch-perfect rant, provocative comment or burning question) may actually be hired actors reading from scripts. I’m not an angry listener, but I play one on radio!
Via Tablet Magazine:
If [the actor] passed the audition, he would be invited periodically to call in to various talk shows and recite various scenarios that made for interesting radio. He would never be identified as an actor, and his scenarios would never be identified as fabricated—which they always were.
“I was surprised that it seemed so open,” the actor told me in an interview. “There was really no pretense of covering it up.”
Curious, the actor did some snooping and learned that Premiere On Call was a service offered by Premiere Radio Networks, the largest syndication company in the United States and a subsidiary of Clear Channel Communications, the entertainment and advertising giant. Premiere syndicates some of the more sterling names in radio, including Rush Limbaugh, Glenn Beck, and Sean Hannity. But a great radio show depends as much on great callers as it does on great hosts: Enter Premiere On Call.
“Premiere On Call is our new custom caller service,” read the service’s website, which disappeared as this story was being reported (for a cached version of the site click here). “We supply voice talent to take/make your on-air calls, improvise your scenes or deliver your scripts. Using our simple online booking tool, specify the kind of voice you need, and we’ll get your the right person fast. Unless you request it, you won’t hear that same voice again for at least two months, ensuring the authenticity of your programming for avid listeners.”
Ensuring the authenticity of your programming… with paid, planted callers.
ruin everything, including sig lines. 
