We have caller ID and if we don't know the number, don't answer. If it is a number that we know is a robocall or telemarketer server, we have been plugging in our fax machine. It then gets "recorded" by their system as a non-number (i.e. no human).
Spoofing your phone number by others is definitely a different problem.
A lot of these calls are robocalls that don't say anything unless it gets a voice response from you. We have signed up on the Do Not Call registry, but there are lists being sold by companies that fly under that rule because a company can share information.