My approach is a little different than to hang-up as quickly as possible, as this is a behaviour that the telephone solictors use to their advantange. In short, I try to soak a call for as long as possible. The best tactic is to be a little bit dumb, but fean interest in whatever the person is calling about. I generally find that getting them to explain each sentance they say about 3 times is about right, before moring on to the next sentance.
Anyway, I answer all calls, and press the button to talk to a human, then try to keep the human on the line for as long as possible.
The cost centre for these automated calls is for a human to talk to me. On at least 4 occasions after being an affible fool for about 20 minutes, without the sales person on the other end, they have said "okay, I get it, you don't want us to call you, and we will put you on our 'do not call list'". At which time they promptly hang up in a huff.
I my numbers, work, cottage/holiday home, mobile, work mobile, and work line now only get about 1 call a month, of which I am more than happy to take, and generally ends with the above result. Previously I used to get 4 or so random unknown calls a day.
I also notice that after calling for a taxi, the number of unwanted calls goes up.