Phone spam?

Tonight I received an odd call from a 866 number:

Me: "Hello"

No response

Me: "Hello, who am I talking to?"

Answ: "I am sorry to disturb you. This message was only to be received by an answering machine."

Apparently this not nothing new. One google search result (telephony phishing) goes back to 2005. Very weird. Why do they want to talk to my answering machine? 

This must be a tactic to circumvent some do-not-call list law.