I was messing around with my phone this weeked and I set the phone to auto answer from the settings menu. I checked my phone a few hours later and from the front lcd I couldn't tell I received a call but when I flipped it open at the bottom it read: auto answer on, then scrolled to say 4 voice memos! So instead of going straight to voicemail the calls went to voice memo. Those that call didn't hear a greeting or even a beep to let them know to record a vm. But I thought it was pretty cool that you could get vm's through the voice memos!
If it is set to auto-answer and answering machine is checked a female voice says "please leave message at tone". It answers pretty quickly, though, after 2 rings I think.