Robo call for vent cleaning etc.  Message left requesting you press 1 to be removed from list. Perhaps a ruse to confirm the line has a live person at the other end.

They call at least once a day. Today i made the mistake of picking up because i was multi-tasking. The caller idea states it is cellphone.

They've called twice without leaving a message.

They called here too..thanks for the explanation.

caller id says: air duct
This number called me. Now they are on the blocked call list.
Thanks to my Panasonic KX-TG7875 for the call block feature!

Recorded message robo call that repeated at least 3 times on my answering machine.  Woman's voice:

"To help you improve your indoor air quality? bla, bla? air duct cleaning? bla, bla ? and a free furnace inspection? bla, bla ? To hear more about this offer please press 1 or press 2 to be removed."

Four things about this that I'm aware of:  

1.  Pre-recorded messages from robo callers are now illegal.
2.  The message states no personal name nor name of the company.
3.  The message gives no call-back number nor company phone number.
4.  My number is on the National Do Not Call list.

All these are verboten.  

The voice sounds vaguely like "Dianne" from The Carpet Cleaning Company but I can't say for sure.  Needless to say, don't press anything to reply or you'll be indicating to the robo calling system that you listen.  It's probably a "service" mass calling company the has many more shyster clients that would love to give you more pitches.  The number is from my caller ID and could be spoofed.  This one is getting reported to the FTC and the NDNC.