I get calls from this number and no one is there. I usually don't answer until the second or third ring, and the way I understand it is that they will outcall to several numbers at a time and when one answers they abandon the others to try later.
When I do get connected to unwanted calls from telemarketers, surveys etc., I usually ask them to please wait a second. Then I set the phone down and just let them wait until they realize that I'm not coming back on the line. Eventually they hang up. Once in a while, if I'm not busy, for amusement I'll talk to them and string them along as long as possible before I turn them away. Time and results are important for these people so I just try to waste a little of it.