I like these approaches. Dependent on the mood I am in I either hang up or wind them up. I work on the principle that I can enjoy wasting their time. I put the call on hands free carry on with whatever I am doing and let them try to sell me things , get me tpo reclaim PPI , check my computer (by the way ultimately admitting you only computer is a slide rule does upset them somewhat)
It even works if part way though the call you actually tell them that that is your sole intention. My record so far was 15 mins in tot he call telling someone that i was going to just keep them on the phone, they stayed on trying to sell me PPI and then i finally got bored at just over 45 minutes and told him i was not interested and hung up.
Just never ever give away any information about you, your bank account password pin numbers etc. The person calling often does not even know who they are calling or the number they have called as they are random numbers called by a computer.
Make things up if you want to wind them up. One book club now has me living at 10 downing street! They could not stop sending books but they coudl do a change of address. Thye did not dare call me a liar. I wonder if the PM's over the years have enjoyed the books?