Had the same thing.  Hang up.

calls, then silence or nothing on voicemail.

they just now did it again as i was posting my last comment

MCIMETRO ACCESS TRANSMISSION SERVICES LLC located in Phoenix
I got one of these calls on my vm - but there was silence. Don't know why they were calling but at least I know who it was.

I live in Canada ..why would a transmission service from Phoenix be calling me and then not even say anything,..my god the world has gone crazy...lol