In the Twilight Zone episode The Dummy, there's a scene where "Jerry and Willie" (Robertson's character and the titular ventriloquist dummy) are performing and it looks like the actor's lips move a bit while he's doing the voice of the dummy.
What surprised me was that the act was very good! So good in fact I thought it was a voice over except for a couple of phrases where I could see lip movement.
I've searched around a bit online, but due to the popularity of the episode most results are synopses.