Dr. Neal Krawetz posted something very useful over at the hackerfactor. Apart from that it's also very entertaining. He is legally recording various cold-calls he gets. Some of them are obvious scams and he now and then messes with them until they hang up. Neal has some very good hints, tips and rules you should be aware of. I am only giving highlights here, you need to read the whole post:
Rule #1: Expect no delay. If you answer the phone and do not hear someone respond to your greeting, then it's virtually guaranteed to be a scam, telemarketer, or political survey.
Rule #2: Identify who is calling. Regardless of who it is, you need to know who you are talking to.
Rule #3: Trust but verify. I don't care who they say they are. Verify the caller!
Rule #4: What do they want? Replies should be very specific. "This is a call regarding your credit card." Which credit card exactly?
Rule #5: NEVER give a confirmation. This is really an important lesson and a hard habit to break. Never give any kind of positive confirmation on the phone until you are absolutely certain who you are talking to. Here is a WRONG way to answer the phone:
Them: Is this Neal Krootz?
Me: Yes this is. How can I help you?
Rule #6: Record the call. I'm always amazed at the number of cold calls that hang up on me when I ask these basic questions. "Who is calling?" *click* "What is your address?" *click*. Any caller who won't give their name or address is a scam. And if they hang up, then it's definitely a scam. Right now, about 50% of callers hang up when I ask for their address.
Here is his post, with several recorded sample calls. Have fun and learn something: