We just received one of these calls - nobody is ever on the line. Clearly this is a machine calling. They are either checking when you are home (not likely if it is a business number) or recording peoples voices (clearly for nefarious reasons, likely for some gov database).
This is how telemarketers get around the "Do not call" list. They route their calls through a dummy US phone # where the CRTC can't touch them. If they ever do have someone on the line, just be exceptionally rude and gross and they will eventually go away. Anyone who calls me like this deserves what they get.