It's an auto-dialer that harvests active phone numbers. If they call and you answer, it usually disconnects ...since you answered, they now know its a "good number". Lists are compiled and sold to marketers worldwide that starts the process all over again; unwanted calls and spam that clogs your inbox.
Called home phone. Caller id says Ft. Myers. As always, I NEVER answer my phone for an unrecognized number. A robo call saying that we won a free cruise. On July 25th another number from the same area code 239-970-8397, same robo call from someone named "Lisa" stating the same crap. We won a free cruise. Sure wish we could track these people down for a "face to face".