Received a call at 9:49am on a Wednesday.  No message left.  I've received several calls in the last week - about one a day - from phone numbers with Orlando, Florida area code (407) and the "545" exchange.  The last four digits are always different, but the same thing occurs:  I don't answer and they don't leave any voicemail message.  ...I'm just blocking them one by one as they come in.

Call received.  No message left.  Caller I.D. only listed the number - no name.

Received a call on my work phone.  Left no message.  Caller ID didn't provide any data except the number.  Unfortunately, I'm unable to block numbers from my work phone...so I'll just let any future calls ring, unanswered.