I don't see talking about what they say on the radios in the games as spoilers, but if you do then this if your warning.
This is for Grand Theft Auto BTW.
The reason I think WCTR becomes Chatterbox is this: WCTR is bought out by Donald Love, and he changes it into Chatterbox. He then began broadcasting it over the country, and kept the hosts etc. (or at least two of them.)
I picked it up by some of the things that Lazlow and his hosts say on Chatterbox. For example, at one point Lazlow talks about being on Chatterbox because he "got fired by the rock station." Now, he would surely have mentioned Entertaining America instead of V Rock as it was his last job.
Then, he gets a call from one of the people who phones up Maurice (it's in one of the previews for Gardening With Maurice). Lazlow says that Gardening With Maurice is on later, which must mean Maurice has been employed by Chatterbox, and has either been stolen by WCTR or Chatterbox actually is WCTR.
Just my thoughts, and it's weird I know. I'm bored, so shoot me.