Those calls

Don't ever hang up

How long can you occupy the time of a nuisance caller?  Think of it as a public service.
Calls about holidays are common at the moment.  One of the tactics that can be used is to agree to answering the survey, provided that you can opt out of any question that you think are personal.
They always agree, and you can proceed to decline to answer each one (after politely explaning why you don't want to give that information).

For instance, this was a recent (real life) conversation:
Caller : Is that Mr JDubya?
Me: Who is calling?
Caller: It's Zoe from <blank> and I'm conducting a survey into holidays.  You could win a prize which would be really great wouldn't it
Me : Yes it would be fantastic, what do I have to do?
Caller: Just answer a few questions.  It is Mr JDubya I am speaking to isn't it?
Me: Who did you say you are?
Caller : It's Zoe from <blank>, Is that Mr JDubya?
How do you spell <blank>?
Caller :<B L A N K >
Me : Let me read that back to you, <L B A K N >
Caller :No, B L A N K
Me : Ok, What's your telephone number?
Caller :You won't be able to call me back
Me : Ok, but I don't know who you are, so I'll answer your questions except where I think it's too personal
Caller :Ok, can you confirm that you are Mr JDubya?
Me : I can't tell you that, it's against the data protection act.
Caller : What?
Me : I can answer your survey questions, but not that one OK?
Caller : OK, First question - If you could have a free holiday anywhere in the world where would it be?
Me : Grimsby
Caller :Anywhere in the world, how about America, Barbados,...
Me : I'd quite like to go to Grimsby.  I've heard the fishing is good.
Caller : Let's put down America for now.
Me : No, You have to put down Grimsby because if you put down anything else it misrepresents my views and violates the Data Protection Act
Caller : OK, but there's lots of places that are good in America, for instance Disneyworld.  Do you have any children?
Me : That's too personal, what's the next question?
Are you married?
Me : Too personal
Caller : Do you own your own home
Me : Too personal
Caller : Have you ever considered timeshare properties or holiday ownership?
Me : Too personal
Caller : Congratulations, you won a holiday in Grimsby.  Can I organise an appointment for you and your wife to collect your prize?
Me : I didn't tell you that I was married.  I might be single.
Caller : If you are single you can pick up the prize yourself.  I have an appointment on Saturday morning at 10:00 is that OK?
Me : Not convenient, do you have anything on a Wednesday morning at say 08:37?
Caller : How about Wednesday at 10:00.  I've booked you in.
Me : I can't do Wednesday.  Can you send me a list of all your appointment dates then I can choose
Caller : Slammed phone down
Me : How rude!