In the old days, we just used a phone booth. Obviously that was before cameras everywhere as well. Now you need a burner phone, that you bought at a convenience store while wearing a disguise, which you changed into from a men’s room somewhere in a different city or, if you are really paranoid, a different continent.
Bottom line: If they want you bad enough, they will find you.
I think they use Internet and IP spoofing to mimic a phone call.