This has to be the worst telespammer ever.  They called something like 4 or 5 times over the course of an hour, went to voicemail, and the proceeded to leave a 3-6 minute long "message" of just background noise.  No real message, just enough noise to keep voicemail from hanging up.

At this point, this is no longer "telemarketing," or any other legal use of telecommunications.  This is a denial-of-service attack, plain and simple.  They are doing nothing but trying to fill up someone's voice mailbox in order to prevent them from receiving legitamate messages.