I picked up and I was totally silent, knowing if it was a real person they'd say "Hello." Waited for a long time while checking for the number and found this site. Eventually it just hung up -- very obviously a machine, and glad to see the info here.
One thing I've been doing lately when I get calls from bill collectors, since some are now calling from local numbers (I think because people like me ignore the toll-free ones -- it's the same old "If - this - is - DAVID - XXXX - please - press - one" etc., just from a local number), is once I get one, I save it in my contacts list under the name Ignore 1, Ignore 2, Ignore 3, etc. so when I get a local area-code call from a number I don't recognize, I don't have to try to remember if it's that bill collector number or someone I met at a bar the night before.