This is probably only new to me.
I have to admit that in my youth I never found the need to give someone a fake phone number. (I was pleased someone actually wanted my phone number.)
On Seinfeld, Elaine gave a fake number regularly, but ended up meeting up with the people who had been getting all her fake calls.
Someone showed me this site which supplies a phone number for you (it's a New York number) that is the "official New York Rejection Line."
They have a "rejection line team" that provides premium rejection services completely free of charge. They recommend you use it at bars, clubs, bathroom walls, in your cell phone as your "private line" as a mysterious voicemail, for creditors, telemarketers, and religious zealots.
What is their business model? Has anyone used this? I am afraid to call.