Well, on Disney's Recess, all of the main kids were called by their 1st names except for Spinelli, whose first name was Ashley, but in her case, she wanted to be called by her last name because she didn't want to be associated with the snooty Ashley clique. In fact, she kept this fact hidden until Randall spilled the beans in the short "First Name Ashley".
As for Futurama's Fry, I think it was a case that Fry wasn't originally going to have a spoken 1st name, but the producers made his first name be Phillip as a tribute to the late Phil Hartman. Plus, Fry is a funnier name than Phillip.
Going back to Cartman, Matt Stone and Trey Parker stated in an interview for Animation Magazine that Cartman was the name of a guy they knew, although the real life Cartman is nothing like the Eric Cartman on the show.