> The first I ever heard of a "calls are coming from inside the house" trope was from a beer commercial with those penguins in it
Are you telling me that you didn't read Scary Stories to Tell in the Dark as a kid?
The wikipedia article lists movies based on that story. I did not know the extended ending, which gets used (and extended further) in When a Stranger Calls.
I wasn't familiar with Janett Christman but it sounds like it's responsible for the trope of being attacked while babysitting, but the threatening phone calls aren't part of it.