I'm at home a lot, so I get a deluge of the annoying phone calls. Most of the time I don't answer, and they don't bother with the machine. So here's my current list on how to deal with them.
Don't be afraid to be rude! I just hang up as soon as I realize what is happening. I figure that somebody real would call back, assuming that there was a problem with the phone line. :)
Indications of something wrong:
A dead delay in connecting. If you have to say 'Hello' twice hang up, you are being sucked to India! Remember that Bell, etc, want to be as cheap as possible. They have automatic war dialers making the call, and recognize a genuine greeting, then they switch to India. Nearly all my problem calls are from India.
Cross-talk and noise. They use really cheap talent. If you hear lots of voices, or funny noises, hang up.
Whiny male Indian voice - hang up.
Too loud, too soft - hang up.
Now, if you are successful, things will taper down, until the Phone-Sex Lady calls you. This is a trained vocal artist who probably charges by the second. She says "Sorry, wrong number" ,you are stunned for a second, and she is gone before you can say "Can't you talk to me some more?". She just reestablishes that you answer the phone, and suddenly you get a ton of the cheap calls again. If she was selling something, I'd listen, but I probably couldn't afford it. :)
Technology improves, and they are getting better with the switching delays. So far, I haven't hung up on the wife yet, but it's getting close!